Oxidative coupling of methane for olefin production

ABSTRACT

The present disclosure provides natural gas and petrochemical processing systems, including oxidative coupling of methane reactor systems that may integrate process inputs and outputs to cooperatively utilize different inputs and outputs in the production of higher hydrocarbons from natural gas and other hydrocarbon feedstocks. The present disclosure also provides apparatuses and methods for heat exchange, such as an apparatus that can perform boiling and steam super-heating in separate chambers in order to reach a target outlet temperature that is relatively constant as the apparatus becomes fouled. A system of the present disclosure may include an oxidative coupling of methane (OCM) subsystem that generates a product stream comprising compounds with two or more carbon atoms, and a dual compartment heat exchanger downstream of, and fluidically coupled to, the OCM subsystem.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/523,032, filed Jul. 26, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/912,104, filed Mar. 5, 2018, now U.S. Pat. No.10,407,361, which is a divisional of U.S. patent application Ser. No.15/487,181, filed Apr. 13, 2017, now U.S. Pat. No. 9,944,573, whichclaims priority to U.S. Provisional Patent Application Ser. No.62/322,190, filed Apr. 13, 2016, U.S. Provisional Patent ApplicationSer. No. 62/341,307, filed May 25, 2016, U.S. Provisional PatentApplication Ser. No. 62/341,308, filed May 25, 2016, U.S. ProvisionalPatent Application Ser. No. 62/379,675, filed Aug. 25, 2016, U.S.Provisional Patent Application Ser. No. 62/397,798, filed Sep. 21, 2016,and U.S. Provisional Patent Application Ser. No. 62/417,102, filed Nov.3, 2016, each of which is entirely incorporated herein by reference.

BACKGROUND

There exists an infrastructure for chemical production throughout theworld. This infrastructure is deployed on virtually every continent,addresses wide ranging industries, and employs a wide variety ofdifferent implementations of similar or widely differing technologies.

SUMMARY

The present disclosure provides systems and methods for reacting methanein an oxidative coupling of methane (“OCM”) process to yield productscomprising hydrocarbon compounds with two or more carbon atoms (“C₂₊compounds”), including propylene.

An aspect of the present disclosure provides a method for producingpropylene, comprising: (a) directing methane (CH₄) and oxygen (O₂) intoan oxidative coupling of methane (OCM) reactor that permits the CH₄ andthe O₂ to react to yield an OCM product stream comprising hydrocarboncompounds with two or more carbon atoms (C₂₊ compounds), includingethylene; (b) directing at least a portion of the OCM product streaminto a separations unit that yields an ethylene stream comprising theethylene from the OCM product stream; (c) directing at least a portionof the ethylene stream from the separations unit into a dimerizationreactor that permits at least a portion of the ethylene to react in adimerization reaction to yield a butene stream comprising one or morebutene compounds; (d) directing at least a portion of the butene streaminto a C₄ separations unit that yields a butene-2 stream comprisingbutene-2 from the at least a portion of the butene stream; and (e)directing at least a portion of the butene-2 stream and at least anotherportion of the ethylene stream into a metathesis reactor that permits atleast a portion of the butene-2 and the ethylene to react to yield ametathesis product stream comprising higher hydrocarbon compounds,including the propylene.

In some embodiments, the method further comprises directing at least aportion of the metathesis product stream into a C₂ separations unit thatseparates the at least a portion of the metathesis product stream to atleast a C₂ stream comprising hydrocarbon compounds with two carbon atoms(C₂ compounds) and a C₃₊ stream comprising hydrocarbon compounds withthree or more carbon atoms (C₃₊ compounds), including at least a portionof the propylene. In some embodiments, the method further comprisesdirecting the C₂ stream into the separations unit. In some embodiments,the method further comprises directing the C₃₊ stream into a C₃separations unit that separates the C₃₊ stream to at least a C₃ streamcomprising propylene and a C₄₊ stream comprising hydrocarbon compoundswith four or more carbon atoms (C₄₊ compounds). In some embodiments, themethod further comprises directing the C₄₊ stream into the C₄separations unit. In some embodiments, the method further comprisesdirecting the propylene from the metathesis product stream into apolypropylene unit that permits the propylene to react to yield apolypropylene product stream comprising polypropylene. In someembodiments, the method further comprises directing at least a portionof the ethylene from the separations unit to the polypropylene unit,wherein the polypropylene unit reacts the at least a portion of theethylene as a co-monomer with the propylene. In some embodiments, amolar ratio of ethylene co-monomer to total monomer and co-monomer isfrom about 0.01:0.99 to about 0.15:0.85. In some embodiments, the molarratio of ethylene co-monomer to total monomer and co-monomer is fromabout 0.08:0.92 to about 0.15:0.85. In some embodiments, (a) furthercomprises directing ethane (C₂H₆) into the OCM reactor. In someembodiments, the method further comprises injecting olefins with five ormore carbon atoms (C₅₊ olefin) into one or more of the separations unit,the dimerization reactor, the C₄ separations unit, and the metathesisreactor. In some embodiments, the at least another portion of ethylenestream is a remainder of the ethylene stream.

Another aspect of the present disclosure provides a system for producingpropylene, comprising: an oxidative coupling of methane (OCM) reactorthat receives methane (CH₄) and oxygen (O₂) and permits the CH₄ and theO₂ to react to yield an OCM product stream comprising hydrocarboncompounds with two or more carbon atoms (C₂₊ compounds), includingethylene; a separations unit that receives at least a portion of the OCMproduct stream and yields an ethylene stream comprising the ethylenefrom the OCM product stream; a dimerization reactor that receives atleast a portion of the ethylene stream and permits at least a portion ofthe ethylene to react in a dimerization reaction to yield a butenestream comprising one or more butene compounds; a C₄ separations unitthat receives at least a portion of the butene stream and yields abutene-2 stream comprising butene-2 from the at least a portion of thebutene stream; and a metathesis reactor that receives at least a portionof the butene-2 stream and at least another portion of the ethylenestream and permits at least a portion of the butene-2 and the ethyleneto yield a metathesis product stream comprising higher hydrocarboncompounds, including the propylene.

In some embodiments, the system further comprises a C₂ separations unitthat receives at least a portion of the metathesis product stream andseparates the at least a portion of the metathesis product stream to atleast a C₂ stream comprising hydrocarbon compounds with two carbon atoms(C₂ compounds) and a C₃₊ stream comprising hydrocarbon compounds withthree or more carbon atoms (C₃₊ compounds) including at least a portionof the propylene. In some embodiments, the separations unit receives theC₂ stream. In some embodiments, the system further comprises a C₃separations unit that receives the C₃₊ stream and separates the C₃₊stream to at least a C₃ stream comprising propylene and a C₄₊ streamcomprising hydrocarbon compounds with four or more carbon atoms (C₄₊compounds). In some embodiments, the C₄ separations unit receives theC₄₊ stream. In some embodiments, the system further comprises apolypropylene unit that receives the propylene from the metathesisproduct stream and permits the propylene to react to yield apolypropylene product stream comprising polypropylene. In someembodiments, the polypropylene unit receives at least a portion of theethylene from the separations unit and reacts the at least a portion ofthe ethylene as a co-monomer with the propylene. In some embodiments, amolar ratio of ethylene co-monomer to total monomer and co-monomer isfrom about 0.01:0.99 to about 0.15:0.85. In some embodiments, the molarratio of ethylene co-monomer to total monomer and co-monomer is fromabout 0.08:0.92 to about 0.15:0.85. In some embodiments, the OCM reactorreceives ethane (C₂H₆). In some embodiments, the at least anotherportion of the ethylene stream is a remainder of the ethylene stream.

Another aspect of the present disclosure provides a system for producinghydrocarbon compounds including propylene, comprising: an oxidativecoupling of methane (OCM) reactor that receives methane (CH₄) and oxygen(O₂) and permits the CH₄ and the O₂ to react to yield an OCM productstream comprising hydrocarbon compounds with two or more carbon atoms(C₂₊ compounds), including ethylene; a separations unit that receives atleast a portion of the OCM product stream and yields an ethylene streamcomprising the ethylene from the OCM product stream; a dimerizationreactor that receives at least a portion of the ethylene stream andpermits at least a portion of the ethylene to react in a dimerizationreaction to yield a butene stream comprising one or more butenecompounds; and a metathesis reactor that receives at least anotherportion of the ethylene stream and at least a portion of the butenestream and permits at least a portion of the one or more butanecompounds and at least another portion of the ethylene to react toproduce a product stream comprising the propylene.

In some embodiments, the metathesis reactor receives an external C₄stream comprising hydrocarbon compounds with four carbon atoms, whereinthe C₄ stream replaces at least a portion of the butane stream from thedimerization unit. In some embodiments, the metathesis reactor isconfigured to (i) produce only ethylene as the final product, (ii)utilize the dimerization reactor to produce butenes as the finalproduct, (iii) produce propylene as a final product, or (iv) use thepropylene to produce polypropylene. In some embodiments, the productstream comprises polymer grade ethylene, polymer grade propylene,chemical grade ethylene, chemical grade propylene, polypropylene, amixture of butenes, or combinations thereof. In some embodiments, the atleast another portion of ethylene is a remainder of the ethylene fromthe ethylene stream.

Another aspect of the present disclosure provides a system for producingmixed butenes, comprising an oxidative coupling of methane (OCM)reactor, a dimerization reactor in fluid communication with the OCMreactor, and a recovery system in fluid communication with thedimerization reactor, which recovery system is for recovering mixedbutenes.

In some embodiments, the mixed butenes comprise at least about 50%butene-2. In some embodiments, the mixed butenes comprise at least about90% butene-2. In some embodiments, the mixed butenes comprise at leastabout 99% butene-2.

Another aspect of the present disclosure provides a system for producingbutene-1, comprising an oxidative coupling of methane (OCM) reactor, adimerization reactor in fluid communication with the OCM reactor, and arecovery unit in fluid communication with the dimerization reactor,which recovery unit recovers the butene-1.

Another aspect of the present disclosure provides a method for producingbutene-1, comprising: (a) directing methane (CH₄) and oxygen (O₂) intoan oxidative coupling of methane (OCM) reactor that permits the CH₄ andthe O₂ to react to yield an OCM product stream comprising hydrocarboncompounds with two or more carbon atoms (C₂₊ compounds), includingethylene; (b) directing at least a portion of the OCM product streaminto a dimerization reactor that permits at least a portion of theethylene to react to produce a dimerization product stream comprisingthe butene-1; and (c) directing the dimerization product stream into aseparations unit that produces a first stream containing un-reactedethylene and a second stream containing the butene-1.

In some embodiments, the method further comprises recycling theun-reacted ethylene to the dimerization reactor. In some embodiments,the method further comprises reacting the butene-1 with ethylene toproduce low linear density polyethylene (LLDPE). In some embodiments,the dimerization reactor contains a catalyst containing titanium.

Another aspect of the present disclosure provides a method for producingbutene-2, comprising: (a) directing methane (CH₄) and oxygen (O₂) intoan oxidative coupling of methane (OCM) reactor that permits the CH₄ andthe O₂ to react to yield an OCM product stream comprising hydrocarboncompounds with two or more carbon atoms (C₂₊ compounds), includingethylene; (b) directing at least a portion of the OCM product steam intoa dimerization reactor that permits at least a portion of the ethyleneto react to produce a dimerization product stream comprising butene-1;and (c) directing the dimerization product stream into ahydroisomerization reactor that converts the butene-1 to the butene-2.

In some embodiments, the method further comprises directing the butene-2and at least a portion of the ethylene to a metathesis reactor toproduce propylene. In some embodiments, the method further comprisesrecycling un-reacted ethylene to the dimerization reactor.

Another aspect of the present disclosure provides a system for producingbutadiene, comprising an oxidative coupling of methane (OCM) reactor, adimerization reactor in fluid communication with the OCM reactor, and aC₄ dehydrogenation unit in fluid communication with the dimerizationreactor.

Another aspect of the present disclosure provides a method for producingbutadiene, comprising: (a) directing methane (CH₄) and oxygen (O₂) intoan oxidative coupling of methane (OCM) reactor that permits the CH₄ andthe O₂ to react to yield an OCM product stream comprising hydrocarboncompounds with two or more carbon atoms (C₂₊ compounds), includingethylene; (b) directing at least a portion of the OCM product streaminto a dimerization reactor that permits at least a portion of theethylene to react to produce a dimerization product stream comprisingbutene-1; and (c) directing the dimerization product stream into a C₄dehydrogenation reactor that converts the butene-1 to the butadiene.

Another aspect of the present disclosure provides a method forperforming an oxidative coupling of methane (OCM) reaction, comprising:(a) heating a first stream comprising methane (CH₄) to a firsttemperature; (b) heating a second stream comprising oxygen (O₂) to asecond temperature, which second temperature is less than the firsttemperature; and (c) mixing the first stream and the second stream toproduce a third stream, which third stream is contacted with an OCMcatalyst to perform an OCM reaction.

In some embodiments, the first stream is natural gas. In someembodiments, the second stream is air. In some embodiments, the firststream and second stream are mixed in (c) prior to performing the OCMreaction. In some embodiments, portions of the third stream having ahigher concentration of O₂ have a lower initial temperature when thesecond temperature is lower than the third temperature, and a maximumtemperature of the OCM reaction in (c) is reduced when the first streamand the second stream is perfectly mixed and/or the second temperatureis substantially equal to the third temperature. In some embodiments,the heat capacity of the second stream is at least about 30% of the heatcapacity of the third stream. In some embodiments, a difference betweenthe first temperature and the second temperature is at least about 20°C. In some embodiments, the first temperature is at most about 550° C.when the first stream comprises greater than about 5 mol % hydrocarboncompounds with two or more carbon atoms (C₂₊ compounds). In someembodiments, the first temperature is at most about 600° C. when thefirst stream comprises less than about 5 mol % hydrocarbon compoundswith two or more carbon atoms (C₂₊ compounds).

Another aspect of the present disclosure provides a method forperforming an oxidative coupling of methane (OCM) reaction, comprising:(a) heating a first stream comprising oxygen (O₂) to a firsttemperature; (b) dividing a second stream comprising methane (CH₄) intoat least two portions and heating each of the at least two portions to adifferent temperature; (c) directing the each of the at least twoportions of the second stream into a different area of a mixer, whichmixer mixes the CH₄ with the first stream to generate mixtures; and (d)contacting the mixtures generated in (c) with an OCM catalyst bed toperform the OCM reaction.

In some embodiments, the first stream is air. In some embodiments, thesecond stream is natural gas. In some embodiments, areas of the mixerinto which the at least two portions of the second stream are directedin (c) are selected to reduce a maximum temperature of the OCM catalystbed during the reaction in (d). In some embodiments, areas of the mixerinto which the at least two portions of the second stream are directedin (c) are selected to bypass a portion of the O₂ further into the OCMcatalyst bed.

Another aspect of the present disclosure provides a method forperforming an oxidative coupling of methane (OCM) reaction, comprising:(a) heating a first stream comprising methane (CH₄) to a firsttemperature; (b) dividing a second stream comprising oxygen (O₂) into atleast two portions and heating each of the at least two portions to adifferent temperature; (c) directing the each of the at least twoportions of the second stream into a different area of a mixer, whichmixer mixes the O₂ with the first stream; and (d) contacting themixtures produced in (c) with an OCM catalyst bed to perform the OCMreaction.

In some embodiments, the first stream is natural gas. In someembodiments, the second stream is air. In some embodiments, areas of themixer into which the at least two portions of the second stream aredirected in (c) are selected to reduce a maximum temperature of the OCMcatalyst bed during the reaction in (d). In some embodiments, areas ofthe mixer into which the at least two portions of the second stream aredirected in (c) are selected to bypass a portion of the O₂ further intothe OCM catalyst bed.

Another aspect of the present disclosure provides a method forperforming an oxidative coupling of methane (OCM) reaction, comprising:(a) providing a first stream comprising methane (CH₄) at a firsttemperature; (b) providing a second stream comprising oxygen (O₂) at asecond temperature; and (c) alternately directing the first stream andthe second stream into an OCM reactor that comprises an OCM catalyst toperform the OCM reaction.

In some embodiments, the second temperature is less than the firsttemperature. In some embodiments, the first stream and the second streamare alternated at a frequency that is varied in response to atemperature measured in the OCM reactor. In some embodiments, less O₂ isdirected into the OCM reactor when the temperature in the OCM reactorapproaches a maximum temperature. In some embodiments, the frequency isbetween about 0.1 and about 10 hertz (Hz). In some embodiments, (c) isperformed with piezo-electric injectors.

Another aspect of the present disclosure provides a method forperforming an oxidative coupling of methane (OCM) reaction, the methodcomprising: (a) providing a first stream comprising methane (CH₄) andoxygen (O₂) at a first temperature; (b) providing a second streamcomprising CH₄ at a second temperature; and (c) alternately directingthe first stream and the second stream into an OCM reactor whichcomprises an OCM catalyst to perform an OCM reaction. In someembodiments, the second stream further comprises O₂.

Another aspect of the present disclosure provides a method forperforming an oxidative coupling of methane (OCM) reaction, comprising:(a) directing a first portion of methane (CH₄) and a first portion ofoxygen (O₂) into a first OCM reactor, wherein the first OCM reactor isan adiabatic reactor; (b) in the first OCM reactor, producing a firstproduct stream comprising hydrocarbon compounds with two or more carbonatoms (C₂₊ compounds) and liberating a first portion of heat, whichfirst portion of heat increases the temperature of the first productstream; (c) directing a second portion of CH₄ and a second portion ofoxygen O₂ into a second OCM reactor, wherein the second OCM reactor isan isothermal reactor; (d) in the second OCM reactor, producing a secondproduct stream comprising hydrocarbon compounds with two or more carbonatoms (C₂₊ compounds) and liberating a second portion of heat, whichsecond portion of heat is removed from the second OCM reactor; and (e)combining the second product stream with the first product stream,wherein the first portion of heat aids in converting ethane (C₂H₆) inthe first and/or second product streams into ethylene (C₂H₄).

In some embodiments, the method further comprises (i) adding C₂H₆ to thefirst product stream, and (ii) converting the C₂H₆ added in (i) intoC₂H₄. In some embodiments, the method further comprises (i) adding C₂H₆to the combined stream in (e), and (ii) converting the C₂H₆ added in (i)into C₂H₄. In some embodiments, the second OCM reactor is a tubularreactor. In some embodiments, the second OCM reactor is a fluidized bedreactor. In some embodiments, the first portion of heat increases thetemperature of the first product stream to at least about 800° C. Insome embodiments, the second portion of heat is removed from the secondOCM reactor such that the temperature of the second product stream isless than about 800° C. In some embodiments, the first OCM reactorconverts between about 10% and about 13% of the first portion of CH₄into C₂₊ compounds. In some embodiments, the first OCM reactor convertsthe first portion of CH₄ into C₂₊ compounds with a C₂₊ selectivity fromabout 55% to about 65%. In some embodiments, the first OCM reactor has aC₂₊ yield from about 6% to about 9%. In some embodiments, the second OCMreactor converts between about 20% and about 22% of the second portionof CH₄ into C₂₊ compounds. In some embodiments, the second OCM reactorconverts the second portion of CH₄ into C₂₊ compounds with a C₂₊selectivity from about 60% to about 70%. In some embodiments, the secondreactor has a C₂₊ yield from about 12% to about 15%. In someembodiments, the first OCM reactor comprises a reaction zone comprisingan OCM catalyst and a post-bed cracking zone in which (e) is performed.In some embodiments, a ratio of the amount of second product stream tothe amount of first product stream in (e) is such that a temperature ofthe combined stream is reduced below about 400° C. following conversionof C₂H₆ into C₂H₄.

Another aspect of the present disclosure provides an apparatus forexchanging heat, the apparatus comprising: a first chamber and a secondchamber; a plurality of tubes configured to contain a process fluid thatflows from an inlet in the first chamber to an exit of the secondchamber, passing through the first chamber and the second chamber; and asteam drum configured to contain a liquid phase and a gas phase of acooling fluid, wherein (i) the steam drum is in fluidic communicationwith the first chamber such that the liquid phase of the cooling fluidis contacted with an exterior of the plurality of tubes in the firstchamber to boil the cooling fluid using heat derived from the processfluid, and (ii) the steam drum is in fluidic communication with thesecond chamber such that the gas phase of the cooling fluid is contactedwith an exterior of the plurality of tubes in the second chamber tosuper-heat the cooling fluid using heat derived from the process fluid.

In some embodiments, the boiled cooling fluid is returned from the firstchamber to the steam drum. In some embodiments, the super-heated coolingfluid is used to provide energy to a chemical process. In someembodiments, the first chamber shares a wall with the second chamber. Insome embodiments, each of the plurality of tubes comprises a first tubeadjoined to a second tube to provide a continuous conduit for theprocess fluid. In some embodiments, the first tube passes through thefirst chamber and the second tube passes through the second chamber, andthe first chamber is adjoined to the second chamber. In someembodiments, leakage of the cooling fluid from the first chamber to thesecond chamber is prevented by a seal, by bonding, welding, or brazingthe first chamber to the second chamber, and/or by expanding each of theplurality of tubes in a joint. In some embodiments, the apparatus doesnot comprise a cross-over duct between the first chamber and the secondchamber. In some embodiments, the first chamber comprises at least oneof (a) a down-comer connected to the steam drum to distribute thecooling fluid over the exterior of the plurality of tubes, (b) a riserconnected to the steam drum to collect the cooling fluid, and (c) abaffle that supports the plurality of tubes and/or guides the coolingfluid from the down-comer to the riser. In some embodiments, theapparatus comprises (a), (b) and (c). In some embodiments, the apparatuscomprises a plurality of down-comers, and each down-corner is controlledby a valve, which valves are capable of modulating an amount of thecooling fluid that is boiled in the first chamber. In some embodiments,the second chamber comprises a plurality of baffles that supports theplurality of tubes and/or directs the cooling fluid over the exterior ofthe plurality of tubes. In some embodiments, the apparatus furthercomprises an atomizer for adding an aerosol of the cooling fluid to thegas phase of the cooling fluid prior to flowing into the second chamber,which atomizer is controlled by a valve that is capable of modulating anamount of the cooling fluid that is super-heated in the second chamber.In some embodiments, the apparatus further comprises a valve that iscapable of modulating an amount of the gas phase of the cooling fluidthat is withdrawn from the steam drum, which valve is capable ofmodulating an amount of the super-heated cooling fluid that is produced.In some embodiments, the cooling fluid flows substantiallyperpendicularly with respect to the process fluid in the first chamber.In some embodiments, the cooling fluid flows substantially co-currentlywith the process fluid in the second chamber. In some embodiments, theprocess fluid is a hot gas. In some embodiments, the cooling fluid iswater. In some embodiments, the first chamber is a fire-tube boiler. Insome embodiments, the second chamber is a fire-tube steam superheater.In some embodiments, the apparatus further comprises a valve,obstruction, or one or more other units capable of controlling thenumber of tubes through which the process fluid flows.

Another aspect of the present disclosure provides a method forexchanging heat, the method comprising: (a) providing a heat exchangercomprising a first chamber and a second chamber; (b) flowing a processfluid into the first chamber at an initial temperature; (c) in the firstchamber, decreasing the initial temperature of the process fluid to anintermediate temperature by boiling a first quantity of a cooling fluidusing a first quantity of heat derived from the process fluid; (d)flowing the process fluid into the second chamber at the intermediatetemperature; and (e) in the second chamber, further decreasing theintermediate temperature of the process fluid to an exit temperature toa target temperature by super-heating the boiled cooling fluid from (b)using a second quantity of heat derived from the process fluid, whereinno more than about 100 milliseconds (ms) of time passes between theprocess fluid reaching the intermediate temperature and initiation ofsuper-heating the boiled cooling fluid.

In some embodiments, no more than about 50 milliseconds (ms) of timepasses between the process fluid reaching the intermediate temperatureand initiation of super-heating the boiled cooling fluid. In someembodiments, no more than about 10 milliseconds (ms) of time passesbetween the process fluid reaching the intermediate temperature andinitiation of super-heating the boiled cooling fluid. In someembodiments, the first chamber and the second chamber share a wall. Insome embodiments, the heat exchanger is operated for at least about 6months without cleaning. In some embodiments, a second quantity of thecooling fluid in thermal communication with the process fluid in (c) isnot boiled. In some embodiments, the method further comprises, when theexit temperature is lower than the target temperature, decreasing thefirst quantity of the cooling fluid that is boiled, thereby increasingthe exit temperature to the target temperature. In some embodiments, theexit temperature is less than the target temperature because the heatexchanger is not fouled. In some embodiments, the method furthercomprises, when the exit temperature is greater than the targettemperature, increasing the first quantity of the cooling fluid that isboiled, thereby decreasing the exit temperature to the targettemperature. In some embodiments, the exit temperature is greater thanthe target temperature because the heat exchanger is fouled. In someembodiments, the cooling fluid is super-heated to at least about 500° C.In some embodiments, a temperature of the process fluid is decreasedfrom the initial temperature to the target temperature within about 250milliseconds (ms).

Another aspect of the present disclosure provides an oxidative couplingof methane (OCM) system, comprising: an OCM subsystem that (i) takes asinput a first feed stream comprising methane (CH₄) and a second feedstream comprising an oxidizing agent, and (ii) generates from themethane and the oxidizing agent a product stream comprising compoundswith two or more carbon atoms (C₂₊ compounds); and a dual compartmentheat exchanger downstream of, and fluidically coupled to, the OCMsubsystem, the dual compartment heat exchanger comprising a firstcompartment and a second compartment, wherein a temperature of theproduct stream entering an inlet of the first compartment is reduced toa target temperature at an outlet of the second compartment, andwherein: (1) the first compartment comprises (i) a first plurality oftubes to direct the process stream through the first compartment, (ii) afirst plurality of baffles, and (iii) a plurality of down-comer pipes,wherein the plurality of down-comer pipes is fluidically coupled to asteam drum configured to generate a saturated steam; and (2) the secondcompartment comprises (i) a second plurality of tubes fluidicallycoupled to the first plurality of tubes, and (ii) a second plurality ofbaffles, wherein the second plurality of baffles is configured to directthe saturated steam in substantially co-current flow with the productstream.

In some embodiments, the dual compartment heat exchanger furthercomprises a tube sheet positioned between the first compartment and thesecond compartment. In some embodiments, the tube sheet is positionedsubstantially perpendicularly with respect to the first plurality oftubes and the second plurality of tubes. In some embodiments, the tubesheet comprises one or more cavities. In some embodiments, the dualcompartment heat exchanger does not comprise a cross-over duct. In someembodiments, the first compartment is at least about 4 meters in length.In some embodiments, the second compartment is at least about 6 metersin length. In some embodiments, the target temperature is less than orequal to about 500° C. In some embodiments, when the system comprises aprocess fouling resistance less than or equal to about 0.003 meterssquared Kelvin per Watts (m² K/W), the product stream exiting the outletof the second compartment reaches the target temperature. In someembodiments, the OCM subsystem comprises a post-bed cracking unit.

Additional aspects and advantages of the present disclosure will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein only illustrative embodiments of thepresent disclosure are shown and described. As will be realized, thepresent disclosure is capable of other and different embodiments, andits several details are capable of modifications in various obviousrespects, all without departing from the disclosure. Accordingly, thedrawings and description are to be regarded as illustrative in nature,and not as restrictive.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE FIGURES

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings or figures (also referred to herein as “FIG.” and“FIGs.”), of which:

FIG. 1 is a schematic illustration of an example oxidative coupling ofmethane (OCM) process;

FIG. 2 is a schematic illustration of addition of ethane to an exampleOCM reactor;

FIG. 3 shows a schematic illustration of an example OCM process that canproduce butene-1;

FIG. 4 shows a schematic illustration of an example OCM process that canproduce propylene using butene-1 as an intermediate;

FIG. 5 shows a schematic illustration of an example OCM processintegrated with dimerization and a metathesis-based propylene productionprocess;

FIG. 6A shows a schematic illustration of an example OCM processintegrated with dimerization and a metathesis-based propylene productionprocess with polypropylene production;

FIG. 6B shows a schematic illustration of an example OCM processintegrated with a metathesis unit to produce propylene using an externalC₄ feedstock;

FIG. 7A shows a schematic illustration of an example OCM processintegrated with dimerization and a metathesis-based propylene productionprocess having a C₂ splitter;

FIG. 7B shows a schematic illustration of an example OCM processintegrated with dimerization and a metathesis-based propylene productionprocess without a C₂ splitter;

FIG. 8 shows a schematic illustration of an example OCM processintegrated with a dimerization, metathesis and polypropylene unit, withintegrated separation section and an optional C₃ splitter;

FIG. 9 schematically illustrates an example system for the oxidativecoupling of methane (OCM);

FIG. 10 shows an example OCM system comprising methane and oxygencontaining gas streams;

FIG. 11A shows a schematic side view of an example OCM reactor designedwith an airfoil-shaped mixer;

FIG. 11B shows a schematic cross sectional side view of an example OCMreactor designed with an airfoil-shaped mixer;

FIG. 12 schematically illustrates an example blade that may be employedfor use as a rib of a mixer;

FIG. 13A shows a schematic of an example reactor with multiple oxygenfeeds injected at different points along a direction perpendicular toflow;

FIG. 13B shows graphs of local mix gas temperature and local mix gaspercent oxygen in a reactor with multiple oxygen feeds injected atdifferent points along a direction perpendicular to flow;

FIG. 14A shows a schematic of an example reactor with multiple methanefeeds and multiple oxygen feeds injected at different points along adirection perpendicular to flow;

FIG. 14B shows graphs of local mix gas temperature and local mix gaspercent oxygen in a reactor with multiple methane feeds and multipleoxygen feeds injected at different points along a directionperpendicular to flow;

FIG. 15 shows an cross section of an example mixer inlet employingspatially differentiated mixing;

FIG. 16 schematically illustrates an example system for the oxidativecoupling of methane (OCM);

FIG. 17 shows a schematic illustration of an example OCM reactor withalkane injections lines for introducing alkanes to the OCM reactors;

FIG. 18 shows an example OCM system combining an adiabatic reactor andan isothermal reactor;

FIGS. 19A-19D are graphs of temperature versus exchanger length fordifferent example heat recovery methods;

FIG. 20 is diagram of two separate example heat exchangers;

FIG. 21 is diagram of an example dual compartment heat exchanger withprocess gas cross-over duct;

FIG. 22 is a diagram of an example dual compartment heat exchangerwithout process gas cross-over duct;

FIG. 23 shows the effect of fouling on steam generation and superheat;

FIG. 24A is a process flow diagram of an example steam generator andsuperheater combination;

FIG. 24B is a process flow diagram of an example steam generator andsuperheater combination with a double flange and gasket;

FIG. 24C is a process flow diagram of an example steam generator andsuperheater combination with a double flange and gasket;

FIG. 25 is a graph of temperature gas exiting an example heat recoverysteam generator (HRSG) versus process fouling resistance;

FIG. 26 is a table of control functions in relation to process foulingresistance;

FIG. 27 is a diagram of an example tick baffle or tube sheet;

FIG. 28 shows an example computer system that is programmed or otherwiseconfigured to regulate OCM reactions; and

FIG. 29 is a block flow diagram of an example system that is configuredto generate olefins, such as ethylene.

DETAILED DESCRIPTION

While various embodiments of the invention have been shown and describedherein, it will be obvious to those skilled in the art that suchembodiments are provided by way of example only. Numerous variations,changes, and substitutions may occur to those skilled in the art withoutdeparting from the invention. It should be understood that variousalternatives to the embodiments of the invention described herein may beemployed.

The term “higher hydrocarbon,” as used herein, generally refers to ahigher molecular weight and/or higher chain hydrocarbon. A higherhydrocarbon can have a higher molecular weight and/or carbon contentthat is higher or larger relative to starting material in a givenprocess (e.g., OCM or ETL). A higher hydrocarbon can be a highermolecular weight and/or chain hydrocarbon product that is generated inan OCM or ETL process. For example, ethylene is a higher hydrocarbonproduct relative to methane in an OCM process. As another example, a C₃₊hydrocarbon is a higher hydrocarbon relative to ethylene in an ETLprocess. As another example, a C₅₊ hydrocarbon is a higher hydrocarbonrelative to ethylene in an ETL process. In some cases, a higherhydrocarbon is a higher molecular weight hydrocarbon.

The term “OCM process,” as used herein, generally refers to a processthat employs or substantially employs an oxidative coupling of methane(OCM) reaction. An OCM reaction can include the oxidation of methane toa higher hydrocarbon and water, and involves an exothermic reaction. Inan OCM reaction, methane can be partially oxidized and coupled to formone or more C₂₊ compounds, such as ethylene. In an example, an OCMreaction is 2CH₄+O₂→C₂H₄+2H₂O. An OCM reaction can yield C₂₊ compounds.An OCM reaction can be facilitated by a catalyst, such as aheterogeneous catalyst. Additional by-products of OCM reactions caninclude CO, CO₂, H₂, as well as hydrocarbons, such as, for example,ethane, propane, propene, butane, butene, and the like.

The term “non-OCM process,” as used herein, generally refers to aprocess that does not employ or substantially employ an oxidativecoupling of methane reaction. Examples of processes that may be non-OCMprocesses include non-OCM hydrocarbon processes, such as, for example,non-OCM processes employed in hydrocarbon processing in oil refineries,a natural gas liquids separations processes, steam cracking of ethane,steam cracking or naphtha, Fischer-Tropsch processes, and the like.

The terms “C₂₊” and “C₂₊ compound,” as used herein, generally refer to acompound comprising two or more carbon atoms. For example, C₂₊ compoundsinclude, without limitation, alkanes, alkenes, alkynes and aromaticscontaining two or more carbon atoms. C₂₊ compounds can includealdehydes, ketones, esters and carboxylic acids. Examples of C₂₊compounds include ethane, ethene, acetylene, propane, propene, butane,and butene.

The term “non-C₂₊ impurities,” as used herein, generally refers tomaterial that does not include C₂₊ compounds. Examples of non-C₂₊impurities, which may be found in certain OCM reaction product streams,include nitrogen (N₂), oxygen (O₂), water (H₂O), argon (Ar), hydrogen(H₂) carbon monoxide (CO), carbon dioxide (CO₂) and methane (CH₄).

The term “small scale,” as used herein, generally refers to a systemthat generates less than or equal to about 250 kilotons per annum (KTA)of a given product, such as an olefin (e.g., ethylene).

The term “world scale,” as used herein, generally refers to a systemthat generates greater than about 250 KTA of a given product, such as anolefin (e.g., ethylene). In some examples, a world scale olefin systemgenerates at least about 1000, 1100, 1200, 1300, 1400, 1500, or 1600 KTAof an olefin.

The term “item of value,” as used herein, generally refers to money,credit, a good or commodity (e.g., hydrocarbon). An item of value can betraded for another item of value.

The term “carbon efficiency,” as used herein, generally refers to theratio of the number of moles of carbon present in all process inputstreams (in some cases including all hydrocarbon feedstocks, such as,e.g., natural gas and ethane and fuel streams) to the number of moles ofcarbon present in all commercially (or industrially) usable ormarketable products of the process. Such products can includehydrocarbons that can be employed for various downstream uses, such aspetrochemical or for use as commodity chemicals. Such products canexclude CO and CO₂. The products of the process can be marketableproducts, such as C₂₊ hydrocarbon products containing at least about 99%C₂₊ hydrocarbons and all sales gas or pipeline gas products containingat least about 90% methane. Process input streams can include inputstreams providing power for the operation of the process, such as withthe aid of a turbine (e.g., steam turbine). In some cases, power for theoperation of the process can be provided by heat liberated by an OCMreaction.

The term “nitrogen efficiency,” as used herein, generally refers to theratio of the number of moles of nitrogen present in all process inputstreams (in some cases including all nitrogen feedstocks, such as, e.g.,air or purified nitrogen) to the number of moles of nitrogen present inall commercially (or industrially) usable or marketable products of theprocess. Such products can include ammonia and other nitrogen productsthat can be employed for various downstream uses, such as petrochemicaluse, agricultural use, or for use as commodity chemicals. Such productscan exclude nitrogen oxides (NOx), such as NO and NO₂. The products ofthe process can be marketable products, such as ammonia and derivativesthereof containing at least about 90% or 99% ammonia or ammoniaderivatives. Process input streams can include input streams providingpower for the operation of the process, such as with the aid of aturbine (e.g., steam turbine). In some cases, power for the operation ofthe process can be provided by heat liberated by a reaction, such as anOCM reaction.

The term “C₂₊ selectivity,” as used herein, generally refers to thepercentage of the moles of methane that are converted into C₂₊compounds.

The term “C₂₊ yield,” as used herein, generally refers to the amount ofcarbon that is incorporated into a C₂₊ product as a percentage of theamount of carbon introduced into a reactor in the form of methane. Thismay generally be calculated as the product of the conversion and theselectivity divided by the number of carbon atoms in the desiredproduct. C₂₊ yield is typically additive of the yield of the differentC₂₊ components included in the C₂₊ components identified, e.g., ethaneyield+ethylene yield+propane yield+propylene yield etc.).

The term “specific oxygen consumption,” as used herein, generally refersto the mass (or weight) of oxygen consumed by a process divided by themass of C₂₊ compounds produced by the process.

The term “specific CO₂ emission,” as used herein, generally refers tothe mass of CO₂ emitted from the process divided by the mass of C₂₊compounds produced by the process.

The term “unit,” as used herein, generally refers to a unit operation. Aunit operation may be one or more basic steps in a process. A unit mayhave one or more sub-units (or sub-systems). Unit operations may involvea physical change or chemical transformation, such as separation,crystallization, evaporation, filtration, polymerization, isomerization,and other reactions. A unit may include one or more individualcomponents. For example, a separations unit may include one or moreseparations columns or an amine unit may include one or more aminecolumns.

The term “methane conversion,” as used herein, generally refers to thepercentage or fraction of methane introduced into the reaction that isconverted to a product other than methane.

The term “airfoil” (or “aerofoil” or “airfoil section”), as used herein,generally refers to the cross-sectional shape of a blade. A blade mayhave one or more airfoils. In an example, a blade has a cross-sectionthat is constant along a span of the blade, and the blade has oneairfoil. In another example, a blade has a cross-section that variesalong a span of the blade, and the blade has a plurality of airfoils.

The term “auto-ignition” or “autoignition,” as used herein in thecontext of temperature, generally refers to the lowest temperature atwhich a substance, given sufficient time, will spontaneously ignitewithout an external source of ignition, such as a flame or spark. Use ofthe term “auto-ignites” with reference to oxygen refers to the amount ofoxygen that reacts with (e.g., combustion reaction) any or allhydrocarbons that are mixed with oxygen (e.g., methane).

The term “substantially equivalent,” as used herein in the context ofmethane concentration, generally means that the methane concentration iswithin approximately plus or minus 80%, 70%, 60%, 50%, 40%, or 30%, andpreferably within plus or minus 20%, 10%, 5%, or less of the methaneconcentration that may be passed into an existing fractionation train ofa gas facility or cracker facility.

The term “quench,” as used herein, generally refers to rapid cooling orreducing of the temperature of a process stream, such as a process gas.The rapid cooling may be performed by a system component, such as a heatexchanger. Quenching may prevent undesired reactions low-temperatureprocesses from occurring.

The term “fouling,” as used herein, generally refers to the accumulationof unwanted material(s) on a surface of a component of a system, such asan inner surface of a heat exchanger. Fouling may cause altered functionto the heat exchanger. Fouling may impede or interfere with the functionof the heat exchanger. Fouling may include precipitation fouling,particulate fouling, corrosion fouling, chemical reaction fouling,solidification fouling, biofouling, composite fouling, or anycombination thereof. Heavily fouled systems may need to be cleaned toremove the fouling layer from the surface of the system component.

OCM Processes

In an OCM process, methane (CH₄) may react with an oxidizing agent overa catalyst bed to generate C₂₊ compounds. For example, methane can reactwith oxygen over a suitable catalyst to generate ethylene, e.g.,2CH₄+O₂→C₂H₄+2H₂O (See, e.g., Zhang, Q., Journal of Natural Gas Chem.,12:81, 2003; Olah, G. “Hydrocarbon Chemistry”, Ed. 2, John Wiley & Sons(2003)). This reaction may be exothermic (ΔH=−280 kJ/mol) and occur atvery high temperatures (e.g., >450° C. or >700° C.). Non-selectivereactions that can occur include (a) CH₄+2O₂→CO₂+2 H₂O and (b)CH₄+½O₂→CO+2H₂. These non-selective reactions may also be exothermic,with reaction heats of −891 kJ/mol and −36 kJ/mol respectively. Theconversion of methane to COx products may be undesirable due to bothheat management and carbon efficiency concerns.

Experimental evidence suggests that free radical chemistry may beinvolved. (Lunsford, J. Chem. Soc., Chem. Comm., 1991; H. Lunsford,Angew. Chem., Int. Ed. Engl., 34:970, 1995). In the reaction, methane(CH₄) may be activated on the catalyst surface, forming methyl radicalswhich then couple on the surface or in the gas phase to form ethane(C₂H₆), followed by dehydrogenation to ethylene (C₂H₄). The OCM reactionpathway can have a heterogeneous/homogeneous mechanism, which involvesfree radical chemistry. Experimental evidence has shown that an oxygenactive site on the catalyst activates the methane, removes a singlehydrogen atom and creates a methyl radical. Methyl radicals may react inthe gas phase to produce ethane, which may be either oxidative ornon-oxidatively dehydrogenated to ethylene. The main reactions in thispathway can be as follows: (a) CH₄+O⁻→CH₃*+OH⁻; (b) 2CH₃*→C₂H₆; (c)C₂H₆+O⁻→C₂H₄+H₂O. In some cases, to improve the reaction yield, ethanecan be introduced downstream of the OCM catalyst bed and thermallydehydrogenated via the following reaction: C₂H₆→C₂H₄+H₂. This reactionis endothermic (ΔH=144 kJ/mol), which can utilize the exothermicreaction heat produced during methane conversion. Combining these tworeactions in one vessel can increase thermal efficiency whilesimplifying the process.

Catalysts for OCM, may include, e.g., various forms of iron oxide, V₂O₅,MoO₃, Co₃O₄, Pt—Rh, Li/ZrO₂, Ag—Au, Au/Co₃O₄, Co/Mn, CeO₂, MgO, La₂O₃,Mn₃O₄, Na₂WO₄, MnO, ZnO, and/or combinations thereof, on varioussupports. A number of doping elements may be used in combination withthe above-mentioned catalysts.

Various limitations of the conventional approach to C—H bond activationmay limit the yield of OCM reaction under practical operatingconditions. For example, publications from industrial and academic labshave shown characteristic performance of high selectivity at lowconversion of methane, or low selectivity at high conversion (J. A.Labinger, Cat. Lett., 1:371, 1988). Limited by thisconversion/selectivity threshold, no OCM catalyst has been able toexceed 20-25% combined C₂ yield (i.e., ethane and ethylene). Inaddition, almost all such reported yields required extremely highreactor inlet temperatures (>800° C.). Catalysts and processes adaptedfor performing OCM reaction at substantially more practicabletemperatures, pressures and catalyst activities have been described inU.S. Patent Publication Nos. 2012/0041246, 2013/0023709, 2013/0165728,2013/0158322, 2014/0121433, 2014/0274671, and 2015/0314267, each ofwhich is incorporated herein by reference in its entirety for allpurposes.

An OCM reactor can include a catalyst that facilitates an OCM process.The catalyst may include a compound including at least one of an alkalimetal, an alkaline earth metal, a transition metal, and a rare-earthmetal. The catalyst may be in the form of a honeycomb, packed bed, orfluidized bed. In some embodiments, at least a portion of the OCMcatalyst in at least a portion of the OCM reactor can include one ormore OCM catalysts and/or nanostructure-based OCM catalyst compositions,forms and formulations. Examples of OCM reactors, separations for OCM,and OCM process designs are described in U.S. Patent Publication Nos.2013/0225884, 2014/0107385, 2014/0012053, and 2015/0152025, each ofwhich is incorporated herein by reference in its entirety for allpurposes. An OCM reactor can be adiabatic or substantially adiabatic(including, for example, a post-bed cracking unit). An OCM reactor canbe isothermal or substantially isothermal.

With reference to FIG. 1, natural gas 100 and ethane 102 can enter theprocess through a de-sulfurization module (or unit) 104, which can flowinto a process gas compression module 106 where water can be removed.OCM product gas can be added to the process gas compression module 106as well. A process gas cleanup module 108 can remove carbon dioxide(CO₂), some or all of which can be taken to a methanation module 110.Following cleanup, the process gas can flow into a first separationsmodule 112 that removes C₂₊ compounds from the process gas stream. Theremaining process gas can flow to the methanation module 110 and/or afired heater (e.g., to heat incoming OCM gas streams 114). The C₂₊compounds can be fractionated in a second separations module 116 toproduce ethylene (C₂H₄) 118, C₃ compounds 120, and C₄₊ compounds 122 forexample. The second separations module 116 can produce an ethane (C₂H₆)stream 126 that can be returned to the OCM reactor 128. At the OCMreactor 128, oxygen 130 can be reacted with methane from the methanationmodule 132. Outside boundary limits (OSBL) systems may include a steamsystem, a boiler feed water system and a cooling water system.

The OCM reactor can perform the OCM reaction and a post-bed cracking(PBC) reaction, as described in U.S. Patent Publication No.2015/0152025, which is incorporated herein by reference in its entirety.With reference to FIG. 2, the OCM reactor 200 can have an OCM reactionsection 202 and a PBC section 204. Methane 206 (e.g., from natural gas)and oxygen 208 can be injected (via a mixer) into the OCM reactionregion (which comprises an OCM catalyst). The OCM reaction may beexothermic and the heat of reaction can be used to crack additionalethane 210 that can be injected into the PBC region 204. In some cases,yet more ethane 212 can also be injected into the OCM reaction region202 and/or the methane feed is supplemented with ethane or other C₂₊alkanes (e.g., propane or butane). The OCM reactor may produce an OCMeffluent 214.

The relative amounts of supplemental ethane 210 and 212 can be varied toachieve a range of product outcomes from the system. In some cases, noethane is injected into the OCM reaction region 202 (referred to hereinas Case-1). Another example presented herein has 3.5 mol % ethaneinjected into the OCM region (referred to herein as Case-2). Someprocess design results are presented in Table 1.

TABLE 1 Examples of various amounts of ethane in OCM feed Case-1 Case-2Natural gas consumed (MMSCFD) 15.5 16 Ethane consumed (MMSCFD) 2.2 8.3[Ethane] at inlet (mol %) 0.07 3.5 [Ethylene] at outlet (mol%) 3.6 4.9C₂ products (kTa) 85 115 C₃ products (kTa) 10.3 21.1 C₄₊ products (kTa)2.7 2.5 O₂ consumed (ton/ton ethylene) 2.2 1.8 CO₂ produced from OCM(ton/ton ethylene) 0.9 0.7 CO₂ produced from fired heater (ton/tonethylene) 0.6 0.4

In some cases, an amount of hydrogen (H₂) exiting the OCM reactor isrelatively higher for cases having relatively more ethane injection(e.g., 8% H₂ for Case-1 and about H₂ 10% for Case-2). The amount ofethane that can be injected can be limited by the desired temperatureexiting the OCM reaction region 202 or the OCM reactor 214.

Methane can be combined with a recycle stream from downstream separationunits prior to or during introduction into an OCM reactor. In the OCMreactor, methane can catalytically react with an oxidizing agent toyield C₂₊ compounds. The oxidizing agent can be oxygen (O₂), which maybe provided by way of air or enriched air. Oxygen can be extracted fromair, for example, in a cryogenic air separation unit.

To carry out an OCM reaction in conjunction with some catalytic systems,the methane and oxygen containing gases may need to be brought up toappropriate reaction temperatures, e.g., in excess of 450° C. for somecatalytic OCM processes, before being introduced to the catalyst, inorder to allow initiation of the OCM reaction. Once that reaction beginsor “lights off,” then the heat of the reaction may be sufficient tomaintain the reactor temperature at appropriate levels. Alternatively oradditionally, these processes may operate at a pressure aboveatmospheric pressure, such as in the range of about 1 to 30 bars(absolute).

Once formed, C₂₊ compounds can be subjected to further processing togenerate one or more desired or otherwise predetermined chemicals. Insome situations, alkane components of the C₂₊ compounds are subjected tocracking in an OCM reactor or a reactor downstream of the OCM reactor toyield other compounds, such as alkenes (or olefins). See, e.g., U.S.Patent Publication No. 2015/0152025, which is entirely incorporatedherein by reference.

The OCM effluent can be cooled after the conversion to ethylene hastaken place. The cooling can take place within a portion of the OCMreactor and/or downstream of the OCM reactor (e.g., using at least about1, 2, 3, 4, 5 or more heat exchangers). In some cases, a heat exchangeris a heat recovery steam generator (HRSG), such as the apparatusdescribed herein. Cooling the OCM effluent suitably rapidly and to asuitably low temperature can prevent undesirable reactions fromoccurring with the OCM effluent, including, but not limited to theformation of coke or other by-products.

In some embodiments, the OCM effluent is cooled to a target temperatureof less than or equal to about 700° C., 650° C., 600° C., 550° C., 500°C., 450° C., 400° C., 350° C., 300° C., ° C., 200° C., or less. In somecases, the OCM effluent is cooled to the target temperature less than orequal to about 1 second, 900 milliseconds (ms), 800 ms, 700 ms, 600 ms,500 ms, 400 ms, 300 ms, 200 ms, 100 ms, 80 ms, 60 ms, 40 ms, 20 ms, orless of the production of the desired or otherwise predeterminedconcentration of a compound (e.g., ethylene) in the OCM reaction.

In some situations, an OCM system generates ethylene that can besubjected to further processing to produce different hydrocarbons withthe aid of one or more conversion processes (or systems). Such a processcan be part of an ethylene to liquids (ETL) process flow comprising oneor more OCM reactors, separations units, and one or more conversionprocesses for generating higher molecular weight hydrocarbons. Theconversion processes can be integrated in a switchable or selectablemanner in which at least a portion or all of the ethylene containingproduct can be selectively directed to at least about 1, 2, 3, 4, 5, 6,7, 8, 9, 10, or more different process paths to yield as many differenthydrocarbon products. An example OCM and ETL (collectively “OCM-ETL”herein) is provided in U.S. Patent Publication No. 2014/0171707, whichis entirely incorporated herein by reference.

An aspect of the present disclosure provides OCM processes that areconfigured to generate olefins (or alkenes), such as ethylene, propylene(or propene), butylenes (or butenes), etc. An OCM process can be astandalone process or can be integrated in a non-OCM process, such as anatural gas liquid(s) (NGL or NGLs) or gas processing system.

Reference will now be made to the figures, wherein like numerals referto like parts throughout. It will be appreciated that the figures andfeatures therein are not necessarily drawn to scale. In the figures, thedirection of fluid flow between units is indicated by arrows. Fluid maybe directed from one unit to another with the aid of valves and a fluidflow system. In some examples, a fluid flow system can includecompressors and/or pumps, as well as a control system for regulatingfluid flow, as described elsewhere herein.

In some cases, the process equipment is sized to accommodate a range ofamounts of additional ethane such that the process is flexible. Forexample, more ethane can be injected into the process when the price ofethane is relatively cheap in comparison to the price of natural gas(e.g., low frac spread).

The ethane can be mixed with the natural gas and recycled to the OCMunit. The ethane can go straight to the OCM reactor, optionally througha separate de-sulfurization module. Injection of ethane through aseparate de-sulfurization module can reduce the load in the recycle loopof the process and/or give additional production capacity keeping thesame recirculation rate. The purge gas from the process can be used forfuel gas to the fired heater or sales gas.

The concentration of ethane in the feed to the OCM reactor can be anysuitable value, including greater than or equal to about 0.0 mol %, 0.25mol %, 0.5 mol %, 0.75 mol %, 1.0 mol %, 1.25 mol %, 1.5 mol %, 1.75 mol%, 2.0 mol %, 2.25 mol %, 2.5 mol %, 2.75 mol %, 3.0 mol %, 3.25 mol %,3.5 mol %, 3.75 mol %, 4.0 mol %, 4.25 mol %, 4.5 mol %, 4.75 mol %, 5.0mol %, 25 mol %, 5.5 mol %, 5.75 mol %, 6.0 mol %, 7.0 mol %, 8.0 mol %,9.0 mol %, 10.0 mol % or more. In some cases, the concentration ofethane in the feed to the OCM reactor is less than or equal to about 25mol %, 20 mol %, 15 mol %, 10 mol %, 9 mol %, 8 mol %, 7 mol %, 6 mol %,5 mol %, 4 mol %, 3 mol %, 2 mol %, 1 mol %, 0.8 mol %, 0.6 mol %, 0.4mol %, 0.2 mol %, 0.1 mol % or less. In some cases, the concentration ofethane in the feed to the OCM reactor is between any of the two valuesdescribed above, for example, between about 0.01 mol % to about 5 mol %.

The systems and methods of the present disclosure can becarbon-efficient and/or energy-efficient. In some cases, the systems ormethods of the present disclosure have a carbon efficiency of at leastabout 50%, at least about 55%, at least about 60%, at least about 65%,at least about 70%, at least about 75%, at least about 80%, at leastabout 85%, at least about 90%, or more. In some cases, a system of thepresent disclosure or method for use thereof has a ratio of all carbonatoms output from the system as hydrocarbons to all carbon atoms inputto the system of at least about 0.40, at least about 0.50, at leastabout 0.55, at least about 0.60, at least about 0.65, at least about0.70, at least about 0.75, at least about 0.80, at least about 0.85, atleast about 0.90, at least about 0.95, or more.

In some cases, the systems or methods of the present disclosure have acarbon efficiency of between about 50% and about 85%, between about 55%and about 80%, between about 60% and about 80%, between about 65% andabout 85%, between about 65% and about 80%, or between about 70% andabout 80%. In some cases, a system of the present disclosure or methodfor use thereof has a ratio of all carbon atoms output from the systemas hydrocarbons to all carbon atoms input to the system of between about0.50 and about 0.85, between about 0.55 and about 0.80, between about0.60 and about 0.80, between about 0.65 and about 0.85, between about0.65 and about 0.80, or between about 0.70 and about 0.80.

In some cases, the systems and methods combine OCM reaction, post-bedcracking (PBC), separations and methanation reactions. The separationscan include oligomerization of ethylene to C₃₊ compounds, which are moreeasily separated as described in PCT Patent Publication No.WO/2015/105911, which is incorporated herein by reference in itsentirety. Additional details of OCM reactor and process design can befound in PCT Patent Publication Nos. WO/2015/081122 and WO/2015/106023,each of which is incorporated herein by reference in their entirety.

In an aspect, provided herein is a method for performing oxidativecoupling of methane (OCM). The method can comprise (a) reacting oxygen(O₂) with methane (CH₄) to form heat, ethylene (C₂H₄) and optionallyethane (C₂H₆), hydrogen (H₂), carbon monoxide (CO) or carbon dioxide(CO₂); (b) reacting the heat produced in (a) with ethane (C₂H₆) to formethylene (C₂H₄) and hydrogen (H₂); (c) performing at least one of (i)enriching the ethylene (C₂H₄) produced in (a) and (b) or (ii)oligomerizing the ethylene (C₂H₄) produced in (a) and (b) to produce C₃₊compounds and enriching the C₃₊ compounds; and (d) reacting the hydrogen(H₂) produced in (a) and (b) with carbon monoxide (CO) and/or carbondioxide (CO₂) to form methane (CH₄).

In another aspect, provided herein is a system for performing oxidativecoupling of methane (OCM). The system can comprise an OCM reactor thatpermits oxygen (O₂) and methane (CH₄) to react in an OCM process to formheat, ethylene (C₂H₄) and optionally ethane (C₂H₆), hydrogen (H₂),carbon monoxide (CO) or carbon dioxide (CO₂). The system can furthercomprise a cracking vessel in fluid communication with the OCM reactor,which cracking vessel may utilize the heat produced in the OCM reactorto convert ethane (C₂H₆) into ethylene (C₂H₄) and hydrogen (H₂). Thesystem can further comprise a separations module in fluid communicationwith the cracking vessel. The separations module may (i) enrich theethylene (C₂H₄) produced in the OCM reactor and the cracking vessel or(ii) oligomerize the ethylene (C₂H₄) produced in the OCM reactor and thecracking vessel to produce C₃₊ compounds and enriches the C₃₊ compounds.The system can further comprise a methanation reactor in fluidcommunication with the separations module. The methanation reactor maypermit the hydrogen (H₂) produced in the OCM reactor and the crackingvessel to react with carbon monoxide (CO) and/or carbon dioxide (CO₂) toform methane (CH₄).

In some cases, the ethane (C₂H₆) that is cracked in the cracking vesselis produced in the OCM reactor. In some instances, at least some of theethane (C₂H₆) that is cracked is in addition to the ethane (C₂H₆) thatwas produced in the OCM reactor. In some cases, the OCM reactor producesethane (C₂H₆), hydrogen (H₂), carbon monoxide (CO) and carbon dioxide(CO₂). In some cases, the carbon monoxide (CO) and carbon dioxide (CO₂)produced in the OCM reactor is methanated. The separations module canseparate ethylene (C₂H₄) or C₃₊ compounds from methane (CH₄), ethane(C₂H₆), hydrogen (H₂), carbon monoxide (CO) or carbon dioxide (CO₂). Insome instances, the cracking vessel is a portion of the OCM reactor.

The methane formed in the methanation reactor can be returned to the OCMreactor or sold as sales gas. In some embodiments, the OCM reactor hasan OCM catalyst. In some embodiments, the methanation reactor has amethanation catalyst. In some embodiments, the separations modulecomprises an ethylene-to-liquids (ETL) reactor comprising anoligomerization catalyst. At least some of the heat produced in the OCMreactor can be converted to power.

In another aspect, described herein is a method for producing C₂₊compounds from methane (CH₄). The method can comprise: (a) performing anoxidative coupling of methane (OCM) reaction which converts methane(CH₄) and oxygen (O₂) into ethylene (C₂H₄) and optionally ethane (C₂H₆);(b) optionally oligomerizing the ethylene (C₂H₄) to produce C₃₊compounds; and (c) isolating the C₂₊ compounds, wherein the C₂₊compounds may comprise the ethylene (C₂H₄), the ethane (C₂H₆) and/or theC₃₊ compounds. In some cases, the method has a carbon efficiency of atleast about 50%, 60%, 70%, 80%, 905, 95%, or more. In some cases, theisolated the C₂₊ compounds are not pure. In some cases, the isolated theC₂₊ compounds comprise methane, CO, H₂, CO₂ and/or water.

In some cases, the systems or methods of the present disclosure consumeless than or equal to about 150, 140, 130, 120, 110, 100, 95, 90, 85,80, 75, 70, 65, 60, 55, or 50, or less million British Thermal Units(MMBtu) of energy per ton of ethylene (C₂H₄) or C₃₊ compounds enriched.In some cases, the amount of energy consumed by the system includes theenergy content of the feedstock used to make the ethylene (C₂H₄) or C₃₊compounds.

In some cases, the systems or methods of the present disclosure haveconsume between about 65 and about 100, between about 70 and about 110,between about 75 and about 120, between about 85 and about 130, betweenabout 40 and about 80, or between about 50 and about 80 MMBtu of energyper ton of ethylene (C₂H₄) or C₃₊ compounds enriched. In some cases, theamount of energy consumed by the system includes the energy content ofthe feedstock used to make the ethylene (C₂H₄) or C₃₊ compounds.

In some cases, the systems or methods of the present disclosure have aspecific oxygen consumption of greater than or equal to about 1.2, about1.3, about 1.4, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9,about 2.0, about 2.1, about 2.2, about 2.3, about 2.4, about 2.5, about2.6 about 2.7, about 2.8, about 2.9, about 3, about 3.2, about 3.4,about 3.6, about 3.8, about 4.0, or more.

In some cases, the systems or methods of the present disclosure have aspecific oxygen consumption of between about 1.2 and about 2.7, betweenabout 1.5 and about 2.5, between about 1.7 and about 2.3 or betweenabout 1.9 and about 2.1.

In some cases, the systems or methods of the present disclosure have aspecific CO₂ emission of greater than or equal to about 0.5, about 0.6,about 0.7, about 0.8, about 0.9, about 1.0, about 1.1, about 1.2, about1.3, about 1.4, about 1.5, about 1.6, about 2.0, about 2.2, about 2.4,about 2.6, about 2.8, about 3.0, about 3.2, about 3.4, about 3.6, ormore.

In some cases, the systems or methods of the present disclosure have aspecific CO₂ emission of between about 0.5 and about 1.7, between about0.7 and about 1.4, between about 0.8 and about 1.3 or between about 0.9and about 1.1.

In some cases, the systems or methods of the present disclosure producesC₂₊ products, and the C₂₊ products comprise at least about 1%, 2.5%, 5%,7.5%, 10%, 12.5%, 15%, 17.5%, 20% (wt % or mol %) or more C₃₊hydrocarbons.

In some cases, the systems or methods of the present disclosure producesC₂ products and C₃₊ products, and a molar ratio of the C₂ products tothe C₃₊ products is at least or equal to about 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In some cases, themolar ratio of the C₂ products to the C₃₊ products is less than or equalto about 50, 45, 40, 35, 30, 25, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, orless. In some cases, the molar ratio of the C₂ products to the C₃₊products is between any of the two values described above, for example,from about 5 to about 20.

In another aspect, provided herein is a method for producing C₂₊compounds from methane (CH₄), the method comprising: (a) performing anoxidative coupling of methane (OCM) reaction which may convert methane(CH₄) and oxygen (O₂) into ethylene (C₂H₄) and optionally ethane (C₂H₆);(b) optionally oligomerizing the ethylene (C₂H₆) to produce C₃₊compounds; and (c) isolating the C₂₊ compounds, wherein the C₂₊compounds may comprise the ethylene (C₂H₄), the ethane (C₂H₆) and/or theC₃₊ compounds. In some cases, the amount of energy consumed by thesystem includes the energy content of the feedstock used to make theisolated C₂₊ compounds. In some cases, the isolated the C₂₊ compoundsare not pure. In some cases, the isolated the C₂₊ compounds comprisemethane, CO, H₂, CO₂ and/or water.

In some cases, the method consumes less than or equal to about 150, 140,130, 120, 110, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, or lessMMBtu of energy per ton of C₂₊ compounds isolated. In some cases, themethod consumes greater than or equal to about 20, 30, 40, 50, 60, 70,80, 90, 100, or more MMBtu of energy per ton of C₂₊ compounds isolated.In some cases, the method consumes between about 65 and about 100,between about 70 and about 110, between about 75 and about 120, betweenabout 85 and about 130, between about 40 and about 80, or between about50 and about 80 MMBtu of energy per ton of C₂₊ compounds isolated.

In another aspect, provided herein is a method for producing C₂₊compounds from methane (CH₄). The method may comprise performing anoxidative coupling of methane (OCM) reaction using an OCM catalyst. TheOCM reaction may be performed at a set of reaction conditions to converta quantity of methane (CH₄) into ethylene (C₂H₄) at a carbon efficiency.The OCM catalyst may have a C₂₊ selectivity at the set of reactionconditions that is less than the carbon efficiency at the set ofreaction conditions. The set of reaction conditions can include atemperature, a pressure, a methane to oxygen ratio and a gas hourlyspace velocity (GHSV).

In another aspect, provided herein is a method for producing C₂₊compounds from methane (CH₄). The method may comprise (a) performing anoxidative coupling of methane (OCM) reaction using an OCM catalyst at aset of reaction conditions to convert a quantity of methane (CH₄) intoethylene (C₂H₄) and ethane (C₂H₆); and (b) cracking the ethane (C₂H₆) toproduce additional ethylene (C₂H₄). The combined carbon efficiency of(a) and (b) may be greater than the C₂₊ selectivity of the OCM catalystat the set of reaction conditions. The set of reaction conditions caninclude a temperature, a pressure, a methane to oxygen ratio and a gashourly space velocity (GHSV).

In some instances, the C₂₊ selectivity is less than or equal to about70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30% or less. In some instances,the C₂₊ selectivity is greater than or equal to about 20%, 25%, 30%,35%, 40%, 50%, 60%, 70%, 80%, or more. In some cases, the C₂₊selectivity is between any of the two values described herein, forexample, from about 25% to about 50%.

In another aspect, provided herein is a method for producing C₂₊compounds. The method may comprise a) providing a first feedstockcomprising methane (CH₄) and optionally a first amount of ethane (C₂H₆);(b) performing an OCM reaction on the first feedstock to produce an OCMproduct comprising a first amount of ethylene (C₂H₄); (c) combining theOCM product with a second feedstock comprising a second amount of ethane(C₂H₆) to produce a third feedstock; and (d) cracking the thirdfeedstock to produce a second amount of ethylene (C₂H₄). In some cases,the second amount of ethylene includes ethylene produced in (b) and (d).

In some cases, the fraction of the second amount of ethylene (C₂H₄) thatis derived from the first or the second amounts of ethane (C₂H₆) is atleast about 1%, at least about 3%, at least about 5%, at least about 7%,at least about 10%, at least about 15%, at least about 20%, at leastabout 25%, at least about 30%, at least about 35%, at least about 40%,at least about 45%, at least about 50%, at least about 55%, or more.

In some cases, the combined moles of the first amount and second amountof ethane (C₂H₆) divided by the combined moles of the first feedstockand the second feedstock is greater than or equal to about 1%, 3%, 5%,7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or more. Insome cases, the combined moles of the first amount and second amount ofethane (C₂H₆) divided by the combined moles of the first feedstock andthe second feedstock is less than or equal to about 90%, 80%, 70%, 60%,50%, 40%, 30%, 20%, 10% or less.

In some cases, the combined moles of the first amount and second amountof ethane (C₂H₆) divided by the combined moles of the first feedstockand the second feedstock is between about 1% and about 50%, betweenabout 1% and about 40%, between about 1% and about 30%, between about 1%and about 20%, between about 1% and about 15%, between about 1% andabout 10%, or between about 10% and about 50%.

In some cases, the first feedstock is natural gas. In some cases, thefirst feedstock is natural gas supplemented with the first amount ofethane (C₂H₆). In some cases, the first feedstock is natural gas havingpassed through a separations system to substantially remove thehydrocarbons other than methane.

In some cases, the molar percent of ethane (C₂H₆) in methane (CH₄) inthe first feedstock is greater than or equal to about 1%, 3%, 5%, 7%,10%, 15%, 20%, or more.

In some cases, some or all of a methane-containing feed stream (e.g.,natural gas) can be processed in a separation system prior to beingdirected into an OCM reactor. Directing a methane-containing feed streaminto an OCM reactor via a separation system or subsystem rather thaninto an OCM reactor directly can provide advantages, including but notlimited to increasing the carbon efficiency of the process, optimizingthe OCM process for methane processing, and optimizing the post-bedcracking (PBC) process for ethane processing. Such a configuration canresult in higher back-end sizing for the system. In some cases (e.g.,when using high pressure pipeline natural gas as a feedstock, highrecycle ratio), the back-end sizing increase can be reduced ormoderated. The separation system or subsystem can comprise a variety ofoperations including any discussed in the present disclosure, such asCO₂ removal via an amine system, caustic wash, dryers, demethanizers,deethanizers, and C₂ splitters. In some cases, all of the methane andethane in the methane-containing feed stream (e.g., natural gas) passesthrough a separations system or separations subsystem prior to passingthrough an OCM reactor. Some or all of the ethane from the feed streamcan be directed from the separation system or subsystem into the inletof an OCM reactor or into a post-bed cracking (PBC) unit.

In some configurations, an OCM system can be operated in a cycle, withat least some of the products from one unit or subsystem being processedor reacted in the next unit or subsystem. For example, oxygen (O₂) andmethane (CH₄) feed can be provided to an OCM reactor, which produces anOCM product stream comprising ethane (C₂H₆), ethylene (C₂H₄), carbonmonoxide (CO) and/or carbon dioxide (CO₂), and heat. The OCM productstream can then be fed into an ethane conversion subsystem (e.g., acracking vessel or an ethane cracker) in fluid communication with theOCM reactor. The ethane conversion subsystem can also receive anadditional C₂H₆ stream. The ethane conversion subsystem can convert C₂H₆(e.g., crack C₂H₆ to C₂H₄) with the aid of the heat liberated by the OCMreaction. The heat can also be used to crack the C₂H₆ in the additionalC₂H₆ stream. A C₂H₄ product stream can then be directed from the ethaneconversion subsystem into a separations module in fluid communicationwith the ethane conversion subsystem. The separations module can enrichproducts such as C₂H₄ in the product stream. The separations module canalso oligomerize C₂H₄ to form compounds comprising three or more carbonatoms (C₃₊ compounds). An enriched product stream enriched in C₂H₄and/or C₃₊ compounds can be recovered from the separations module. Alights stream comprising components such as hydrogen (H₂) (e.g.,hydrogen generated from the cracking of C₂H₆) and CO and/or CO₂ can berecovered from the separations module and directed into a methanationreactor in fluid communication with the separations module. Themethanation reactor can react H₂ with CO and/or CO₂ to form a methanatedstream comprising CH₄. The methanated stream can then be directed intothe OCM reactor to provide additional methane for the OCM process. Insome cases, energy generated in the methane conversion section in theform of high pressure steam, high temperature steam, heat, electricity,heat transferred via gas-gas heat exchanger, heat transferred viagas-liquid heat exchanger, or other forms, can be used to provide all ofthe energy and power required to run the entire plant or system.

In some cases, a cyclical system or process can operate with a carbonefficiency such as those discussed in this disclosure. For example, sucha system or process can operate with a carbon efficiency of greater thanor equal to about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or more.In some cases, such a system or process can operate with a carbonefficiency of between about 50% and about 85%, between about 55% andabout 80%, between about 60% and about 80%, between about 65% and about85%, between about 65% and about 80%, or between about 70% and about80%.

In some cases, such a system or process (or method) can operate suchthat a ratio of all carbon atoms output from the system as hydrocarbonsto all carbon atoms input to the system is greater than or equal toabout 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, or more. Insome cases, such a system or process can operate such that a ratio ofall carbon atoms output from the system as hydrocarbons to all carbonatoms input to the system is between about 0.50 and about 0.85, betweenabout 0.55 and about 0.80, between about 0.60 and about 0.80, betweenabout 0.65 and about 0.85, between about 0.65 and about 0.80, or betweenabout 0.70 and about 0.80.

An example process can comprise an OCM unit, a process gas compressor, aprocess gas cleanup unit, a cryogenic separations unit, a fractionationunit, a methanation unit, and a sulfur-removal unit. An oxygen streammay be fed into the OCM unit, along with a C₁ recycle stream from themethanation unit and a C₂ recycle stream from the fractionation unit. Anatural gas stream and an ethane stream may be fed into the sulfurremoval unit. Output from the OCM unit and the sulfur removal unit maybe directed into the process gas compressor, and then into the processgas cleanup unit, which removes a CO₂ stream. The remaining productstream may be directed into the cryogenic separations unit, where lightcomponents including H₂ and CO or CO₂ may be directed into themethanation unit, and the remaining product stream, including ethyleneand other C₂₊ compounds, may be directed into the fractionation unit.The fractionation unit may be configured to separate an ethylene streamand a C₃₊ compound stream comprising C₃ compounds, C₄ compounds, and C₅₊compounds, as well as the C₂ recycle which may be directed back to theOCM unit. The methanation unit may convert the light components intomethane, a first portion of which may be recycled to the OCM unit and asecond portion of which may be output as sales gas. The operating flowrates for the input streams may be as follows: 20.3 MT/h of oxygen, 16.0MT/h of natural gas, and 2.9 MT/h of ethane. The operating flow ratesfor the output streams may be as follows: 9.0 MT/h of ethylene, 1.4 MT/hof C₃₊ compounds, 4.3 MT/h of sales gas, and 8.2 MT/h of CO₂. Thecorresponding carbon content of the input streams may be 972 kmol/h ofcarbon in the natural gas stream, and 194 kmol/h of carbon in the ethanestream. The corresponding carbon content of the output streams may be642 kmol/h of carbon in the ethylene stream, 96 kmol/h of carbon in theC₃₊ compounds stream, 247 kmol/h of carbon in the sales gas stream, and181 kmol/h of carbon in the CO₂ stream. The amount of carbon input tothe system may be 1166 kmol/h, and the amount of carbon output from thesystem in hydrocarbon products (e.g., excluding CO₂) is 985 kmol/h, fora resulting carbon efficiency of 84.5%.

Reaction heat (e.g., OCM reaction heat) can be used to supply some,most, or all of the energy used to operate systems and perform processesof the present disclosure. In some examples, reaction heat can be usedto supply greater than or equal to about 50%, 55%, 60%, 65%, 70%, 75%,80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100% of energy for operatingsystems and performing processes of the present disclosure. For example,the reaction heat can be used to supply at least about 80% or 90% of allof the energy for operating systems or processes of the presentdisclosure. This can provide for an efficient, substantiallyself-contained system with reduced or even minimum external energyinput.

Integration of OCM Processes with Other Chemical Processes

The present disclosure provides systems and methods for integrating OCMsystems and methods with various chemical processes, such as methanol(MeOH) production, chlorine (Cl₂) and sodium hydroxide (NaOH) production(e.g., chloralkali process), vinylchloride monomer (VCM) production,ammonia (NH₃) production, processes having syngas (e.g., mixtures ofhydrogen (H₂) and carbon monoxide (CO) in any proportion), olefinderivative production, or combinations thereof.

As will be appreciated, the capital costs associated with each of thefacility types described above can run from tens of millions to hundredsof millions of dollars each. Additionally, there are inputs and outputs,of these facilities, in terms of both energy and materials, which mayhave additional costs associated with them, both financial and otherwisethat may be further optimized in terms of cost and efficiency. In somecases, because different facilities tend to be optimized for theparticularities (e.g., products, processing conditions) of the market inwhich they exist, they tend to be operated in an inflexible manner, insome cases without the flexibility or option to optimize for their givenmarket. The present inventors have recognized surprising synergies whenintegrating OCM with the aforementioned chemical processes which canresult in improved economics and/or operational flexibility.

In some cases, the OCM processes described herein are integrated with anolefin oligomerization process, such as an ethylene-to-liquids (“ETL”)process as described in U.S. Patent Publication Nos. 2014/0171707 and2015/0232395, each of which is incorporated herein by reference in itsentirety for all purposes.

In some instances, the OCM process can be sized to fit the needs of anethylene derivatives plant. Such a synergy can liberate the derivativesproducer from being a merchant buyer of ethylene, allowing the producermore ethylene cost and supply certainty. Examples of ethylenederivatives include polyethylene, including low-density polyethylene(LDPE), linear low-density polyethylene (LLDPE), and high-densitypolyethylene (HDPE). Additional ethylene derivatives may includeethylbenzene, styrene, acetic acid, vinylacetate monomer, ethylenedichloride, vinylchloride monomer, ethylene oxide, alpha olefins andcombinations thereof.

Integration of OCM Processes with a Butene Process

OCM processes can be integrated with processes for the production ofButenes. Polymer grade Ethylene from the OCM process can be a feedstockto a dimerization system. The dimerization system may comprise adimerization Reactor loop, and associated recovery and purificationsystems. The ethylene may be dimerized to a C₄ olefin, i.e., butene-2,butene-1, iso-butene, and/or some higher hydrocarbons like hexene andoctene. Selectivity to butene-2 can be as high as about 90%, 91%, 92%,93%, 94%, 95%, or more. The dimerization reactor outlet, can be treatedto recover the butene-2, or isomerized to further increase the yield ofbutene-2. The mix butenes product can be used to manufacture sec-butylalcohol (SBA) via hydration. The SBA can be further converted to methylethyl ketones. Alternately, the mix butenes stream can be fed to ametathesis unit, as discussed below, to produce e.g., polymer gradepropylene.

The butene production reaction process can take place in a liquid phasereactor loop. The liquid phase reactor may use a nickel-based phosphinecomplex with an ethyl aluminum dichloride (EADC) co-catalyst. Thereactions may comprise dimerization (to butene-2), butene-1 production,dimerization of ethylene and butene to make hexene, dimerization ofbutenes to form octene and dimerization of hexene and ethylene to formoctene. The catalyst and co-catalyst can be stored in a hexane solvent.Dimerization may be an exothermic reaction that liberates heat. Theliberated heat can be used in the process.

OCM process described herein can be integrated with a process thatproduces butene-1. With reference to FIG. 3, oxygen 300 can be mixedwith methane 302 in an OCM process 304 to produce ethylene 306. Theethylene can be enriched or purified (e.g., to polymer grade ethylene)using any suitable separations operations (e.g., cryogenic separations).The ethylene can be sent to a dimerization unit 308 that producesbutene-1 and some olefinic material such as hexenes and octenes. Anethylene recovery module 310 can be used to separate un-reacted ethylenefrom the dimerization product stream, and optionally recycle 312 theethylene. A butene-1 recovery module 314 can be used to produce anenriched butene-1 stream 316 along with some co-products 318 (e.g., C₆₊compounds). Ethane can be recycled to OCM (not shown). The dimerizationreaction can selectively dimerize ethylene into butene-1 using atitanium based catalyst, which can be recovered in a catalyst recoverymodule 320. The titanium catalyst may be a homogenous catalyst based ona Ziegler-Natta type titanium complex that affords a titanium (IV)cyclic compound in the presence of ethylene, which decomposes tobutene-1 by an intramolecular β-hydrogen transfer reaction (i.e., theAlphabutol™ process). The reaction can be performed at 50° C. and 1-3MPa. The reaction can take place without solvent in a one stage stirredreactor. The reactor effluent can be treated with an amine to deactivatethe catalyst and prevent isomerization of buten-1 to butene-2. Thebutene-1 can be used as a co-monomer in linear low density polyethyleneproduction (LLDPE). An integrated OCM and polyethylene plant with anoption to produce butene-1 required as a co-monomer for LLDPE canproduce high value end-products and provide operational flexibility.

Integration of OCM Processes with a Propylene Process

OCM processes can be integrated with processes for the production ofpropylene, such as metathesis processes.

Metathesis reaction may be a disproportionation reaction, redistributionof fragments of alkenes (olefins) by the scission and regeneration ofcarbon-carbon double bonds. Metathesis unit may comprise a reactorsystem, where the disproportionation reaction takes place, andassociated recovery and purification systems.

The primary feedstocks to the metathesis unit may be a C4 rich streamand ethylene. The product may comprise propylene. The C4 stream maycontain butene-2, butene-1, iso-butene, butanes, or combinationsthereof. Higher concentration of butene-2 (e.g., at least about 30%,40%, 50%, 60%, 70% (wt %, or mol %) or more of the C4 stream may bebutene-2) may be desired in some cases. The propylene produced can be ofpolymer grade and used as a feedstock to produce polypropylene.

Metathesis can be conducted as a vapor phase equilibrium reaction.Metathesis can achieve n-butene conversion greater than or equal toabout 50%, 60%, 65%, 70%, 75%, or more single pass and greater than orequal to about 75%, 80%, 85%, 90%, 95% or more overall conversion.Propylene selectivity may be greater than or equal to about 80%, 82%,84%, 86%, 88%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% orhigher. The reaction can be conducted at isothermal or nearly isothermalconditions, and can be energy neutral.

The metathesis reaction can utilize an ethylene feed and a C4 olefinicfeed to produce propylene via a disproportionation reaction. In theabsence of a C₄ feed, ethylene can be dimerized to produce the C₄olefins used for metathesis. The C₄ olefin can be a butene-2 rich streamwhere the butene-2 content can be greater than or equal to about 75%,80%, 85%, 90%, 93%, 95%, 97%, 99% or more. An OCM module can provide(polymer grade) ethylene to a dimerization unit, and/or to a metathesisunit. The metathesis reactor may contain a section for isomerization ofbutene-1 to butene-2. The product from the metathesis unit can containpredominantly propylene (and varying amounts of unreacted ethylene andbutenes), along with some heavy C₅₊ components. Metathesis units caninclude C₂ separation, C₃ separation and a removal section to remove C₅₊components.

Feedstocks to the metathesis unit can be derived from a steam cracker,which can supply polymer grade ethylene and a C4 stream rich in butenes.Alternatively, polymer grade ethylene can be fed to a dimerizationreactor loop where the ethylene may be dimerized to produce butenes. Theconcentration of butene-2 in the produced butenes can be greater than orequal to about 85%, 88%, 90%, 92%, 95% or more. The dimerization systemintegrated with an OCM may be an ideal situation to produce propyleneusing a metathesis unit. The OCM unit may provide ethylene to both thedimerization unit and the metathesis unit, the capacities are defined sothat the entire Ethylene produced from the OCM is utilized either in thedimerization unit to produce C4 feedstock for the metathesis or as afeedstock to the metathesis unit. Alternatively, the OCM can be sized toproduce extra ethylene, which can be sent to the polypropylene unit as aco-monomer.

In some cases, the dimerization unit can produce predominantly 1-butene(i.e., more butene-1 than butene-2, e.g., at least about 70%, at leastabout 80%, at least about 90%, or at least about 95% butene-2). In somecases, the systems and methods of the present disclosure can have aprocess unit to enhance the production of 2-butene. Non-limitingexamples of such process units may include, a hydroisomerization unit toconvert 1-butene to 2-butene, a selective hydrogenation unit tohydrogenate any butadiene to butenes, or combinations thereof. Thehydroisomerization and hydrogenation units can be within one reactorsystem, or separate reactor systems. In some cases, the isomerization,hydrogenation and separation systems are contained in one vessel (e.g.,tower) or reactor system. Such a system can take in a mixed C4 feed,containing predominantly 2-butene, and some 1-butene, butadiene, andi-butene. The system can hydroisomerize the 1-butene to 2-butene,hydrogenate the butadiene and also separate 2-butene from the rest ofthe C4 components which can then be fed to a metathesis reactor. If thedimerization system produces mainly 1-butene, the hydroisomerizationsystem can be a separate reactor system (e.g., that hydroisomerizes andhydrogenates) with an additional separate separation system to separatethe 2-butene from i-butene and remaining butanes and other C4 compounds.

In some cases, the catalytic hydroisomerization takes place under anatmosphere of hydrogen. In some cases, sulfur can be present in eitherthe feed or added to the hydrogen stream as an additive to reduce thehydrogenation tendency of the catalyst and thus increase thehydroisomerization.

FIG. 4 shows an example system of the present disclosure, where theethylene from OCM is the feedstock to the dimerization unit and themetathesis unit. Oxygen 400 and a feedstock comprising methane 402 canbe fed to an OCM reactor 404 to produce ethylene 406. Some of theethylene can be dimerized 408 to produce butene-1 410, which can beisomerized 412 to butene-2 414 using hydrogen 416. The butene-2 can bereacted with additional ethylene in a metathesis reactor 418 to producepropylene 420. In some cases, the system also produces a C4 stream 422that can be recycled or purged.

Some selective hydrogenation of butadienes can take place in theisomerization reactor 412. The isomerization reactor can be followed bya separation module (not shown) which separates the 2-butene to be fedto the metathesis reactor unit 418. In some cases, the up-frontseparation module is not required. In these cases, the C4 product whichcontains mainly 2-butene 414 is fed to the metathesis reactor 418 and afinal separation is carried out on the metathesis effluent 420 and/or422.

In some cases, the system has separate separation modules for OCM andmetathesis. In these cases, an OCM unit can be designed to producepolymer grade ethylene (i.e., using a separations module dedicated tothe OCM effluent into high purity, in some cases polymer gradeethylene). The polymer grade ethylene may be sent to the dimerizationand metathesis unit. Butene-2 can be produced in a dimerization reactor.The butene-2 rich stream and the polymer grade ethylene from the OCMseparation module can go to the metathesis reactor where propylene isproduced. The metathesis section of the process can have its ownseparation module (i.e., separate from the OCM separations module),which produces polymer grade propylene by separating unreacted ethyleneand heavier molecules (such as fuel oil and gasoline). The heaviermolecules can be separated in two separate columns or a single columnand sent for further processing. In some instances, the system producespolymer grade propylene. Maintaining separate OCM and metathesisseparation modules can be advantageous in some instances (in contrastwith integrated separations) with respect to the simplicity ofoperation, sizing of various equipment and economic implicationsthereof.

In some instances, a metathesis unit integrated with an OCM system canhave a common separations and purification system where the productstream from the metathesis unit is routed to the C₂ separations sectionof the OCM module (de-ethanizer). The de-ethanizer overhead can be sentto the C₂ splitter to generate polymer grade ethylene and an ethaneproduct. The ethane product can be recycled to the OCM reactor. A partof the ethylene produced can be sent to the dimerization reactor and theremaining ethylene is sent to the metathesis unit. The de-ethanizerbottoms stream can be sent to a de-propanizer, followed by a C₃ splitterto produce (polymer grade) propylene. The de-propanizer bottoms can besent to a de-butanizer or a de-pentanizer to recover a C₄ raffinate. Insome cases, the butene rich stream from dimerization reactor can beisomerized in a reactive distillation section to convert butene-1 tobutene-2 and separate the butene-2 for the metathesis reactor. Thedebutanizer overhead may be the C4 feed to the metathesis reactor andmay be routed to the metathesis unit. Some treatment may be required toensure the feed purity to the metathesis unit as the catalysts may bevery sensitive to impurities.

In some cases, the C₄ rich stream can be sourced from a refinery or asteam cracker. The C4 stream can also be a crude C4 mix stream or araffinate I or a raffinate II stream. These C4 streams can be sufficientto provide for the C4 requirement of the metathesis unit with nodimerization required. In some cases, the C₄ stream can be mixed withthe C₄ stream from the dimerization reactor. In either case (i.e.,dimerization alone, dimerization plus off gas recovery or only off gasprocessing), the C₄ processing can also include either a selectivehydrogenation unit (SHU) to hydrogenate any C₄ dienes to olefins, or abutadiene recovery unit or a reactive distillation unit or a totalhydrogenation unit to hydrogenate the remaining Cos after butene-2 hasbeen utilized. In some cases, the final product is a C₄ LPG/C₄ raffinatecontaining butanes, and unreacted butenes.

A raffinate stream can directly be fed to the debutanizer in the unit,from where the overhead can be routed to the metathesis reactor. Theoverhead should be predominantly a butene rich stream. The higher thebutene content, lower is the C₄ purge from the system, and lower are therecycle rates. If a mixed crude C₄ stream is available, it can either besubjected to selective hydrogenation unit where the diolefins(butadienes) may be hydrogenated to butenes, or sent to a butadienerecovery unit to recover the butadiene. This may depend on the feedcomposition and the economics of the particular location and thepetrochemical complex configuration. The C₄ purge stream that containsunreacted butenes, butanes and some other C₄s, can be either sent to arefinery or hydrogenated and sent to a cracking furnace or sold as a C₄stream.

In some cases, a C₅₊ stream can be added to the system (e.g., to thedebutanizer). The addition of C₅ components (e.g., pentenes) can furtherincrease the yield of propylene, as the additional pentenes can beconverted to ethylene and propylene in the system.

The integration described herein (e.g.,OCM+dimerization+metathesis+polypropylene) can yield many advantagesfrom a process and economic standpoint. The combined system can have acommon separations and recovery system, a common refrigeration system,and take advantage of an integrated site with respect to utilities andoff-sites. Additionally, the OCM system can generate excess steam forthe entire system.

Operational Flexibility:

The combined system comprising OCM, dimerization, metathesis,polypropylene unit and an option to import C4 stream may provide immenseoperational flexibility which can produce attractive economic returns.All the units can operate at capacity to produce polymer gradepropylene, or polypropylene product. The ethylene produced from OCM canbe routed to the dimerization unit if the C4s are not available (or arenot available as per the entire C4 demand of metathesis). Alternativelyor additionally, the ethylene produced from the OCM can be, wholly or inpart be sold as a polymer grade ethylene product. In the event of highvalue for butenes, the dimerization unit can be operated without themetathesis unit and the butenes can be exported as a product. The systemcan in effect, produce polymer grade ethylene, polymer grade propylene,mixed butenes stream, in the desired ratio depending on the marketconditions, feedstock availability and the product demand. The feedstockmay be natural gas, which makes the system a highly desirable gasmonetizing option.

In some cases, the product can be butadiene. An OCM unit can be operatedwith a dimerization unit, where the dimerization unit is designed toselectively produce butene-1, and the butene-1 can be fed to a C4dehydrogenation unit to produce butadiene.

In some cases, the dimerization unit can produce 1-butene as the mainproduct, and the 1-butene product can be used as a separate productand/or as a co-monomer in linear low-density poly ethylene production,or used as a feedstock to produce butadiene by oxidative dehydrogenationof 1-butene, or produce polypropylene resins, butylene oxide, orsecondary butyl alcohol (SBA) or methyl ethyl ketone (MEK).

Additionally, ethylene from an OCM process can be supplied as aco-monomer for polypropylene production (e.g., 8-15% ethyleneco-monomer). A separations section of an OCM process can handle therecycle streams from a metathesis unit and a polypropylene unit inaddition to the separations for the OCM process itself.

For example, FIG. 5 shows an example schematic for integration of OCMwith metathesis for propylene production. An OCM unit 500 with an OCMreactor 501 and a separations section 502 receives a methane stream 503(e.g., natural gas) and produces an ethylene product stream 504 (e.g.,polymer-grade ethylene). A portion of the ethylene stream can bedirected into a dimerization reactor 505 to produce C₄ products, whichcan then be separated in a C₄ separation unit 506. Butene-2 507 from theC₄ separation unit can be directed into a metathesis reactor 508 alongwith ethylene from the OCM unit. The metathesis product stream can bedirected to a C₂ separation unit 509, with C₂ compounds being sent as arecycle stream to the OCM unit separations section. C₃₊ compounds can bedirected from the C₂ separations unit to a C₃ separations unit 510.Propylene 511 can be recovered from the C₃ separations unit, with C₄₊compounds directed to the C₄ separation unit.

Propylene can be further processed into polypropylene. For example, FIG.6A shows the propylene 511 being directed, along with ethyleneco-monomer 601 from the OCM unit, into a polypropylene unit 602 toproduce polypropylene 603. Polypropylene production can be an optionaladdition to the process shown in FIG. 5.

FIG. 6B shows an example system where enough C₄ compounds are available(e.g., as a C₄ raffinate stream, as a crude C₄ stream, as a concentratedbutene stream, or any combination thereof), such that the dimerizationunit is no longer required to provide the C₄ compounds for metathesis.As shown in FIG. 6B, where like-numbered elements correspond to those inFIG. 6A, the ethylene 504 from the OCM unit 500 can be directly routedto the metathesis reactor 508, with a part of the ethylene optionallybeing routed to the polypropylene unit 602 to be used as a co-monomer.The external C₄ stream 605 can enter the process at various locationsincluding to the debutanizer 506 where the overhead butene rich stream507 can be sent to the metathesis reactor. In some cases, e.g.,depending on the iso-butene and butadiene content of the external C₄stream, the external C₄ stream can be treated further, which is notshown in the FIG. 6B. In some cases, the external C₄ stream is feddirectly to the metathesis unit 508. In some cases, the process canproduce a C₅₊ product stream 610. In some cases, a recycle stream 615from the C₂ separation unit 509 can be returned directly to themetathesis reactor 508 (i.e., rather than the OCM separations module502).

In some cases, the recovery systems are integrated. For example, withreference to FIG. 7A, a case is shown having a C₂ splitter 700 thatproduces enriched ethylene 701 for the metathesis unit 702 and/or thedimerization unit 704. In some cases, the enriched ethylene ispolymer-grade ethylene (which can also be used as a co-monomer in theproduction of polypropylene). In some instances, the C₂ splitter 700 isnot operated at conditions that result in polymer-grade ethylene. Theenriched ethylene stream can comprise greater than or equal to about60%, about 70%, about 80%, about 90%, about 95%, about 99%, or moreethylene by mass.

Continuing with FIG. 7A, reactants 706 (i.e., methane and O₂) can be fedinto an OCM reactor 708 having a catalyst bed 709 and an ethaneconversion section 710. The OCM reactor can produce an OCM effluent 711that goes to a de-methanizer 712. In some cases, there are additionalunits in the OCM process that are not shown, such as compressors, CO₂removal units, drying units, desulfurization units, quenchers and heatexchangers. The de-methanizer overhead 713 can contain C₁ compounds andgo to a methanation unit 714 for conversion into methane and recycle tothe OCM reactor 708. As used herein, the terms “overhead” and “bottoms”do not limit the portion of the separation column from which the streamemerges (e.g., in some cases, the “bottoms” can come out of the middleor top of the separation column).

The de-methanizer bottoms 715 can include C₂₊ compounds and continueinto a fractionation train including a de-ethanizer 716, a de-propanizer717 and a de-butanizer 718. The de-ethanizer overhead 719 can contain C₂compounds and go to a hydrogenation unit 720, which hydrogenation unitcan (selectively) hydrogenate acetylene. As described herein, the C₂compounds can be separated into an enriched ethylene stream (e.g., usingthe C₂ splitter 700), or not separated as shown in FIG. 7B.

The de-ethanizer bottoms 721 can contain C₃₊ compounds and be taken tothe de-propanizer 717. The de-propanizer overhead 722 can contain C₃compounds that can be split in a C₃ splitter 723 into propane 724 andpropylene 725. In some cases, the propylene is polymer-grade. In somecases, the propylene is used to make polypropylene (optionally with anethylene co-monomer, such as derived from the present process, i.e.,from the C₂ splitter 700). In some cases, the propylene 725 is at leastabout 85%, about 90%, about 95%, about 99%, about 99.5%, about 99.9%,about 99.95%, or more pure.

The de-propanizer bottoms 726 can contain C₄₊ compounds and be directedto a de-butanizer 718. The de-butanizer can produce a bottoms stream 727that includes C₅₊ compounds and an overhead stream 728 comprising C₄compounds, which C₄ compounds can be sent to a C₄ splitter 729. The C₄splitter can produce a plurality of streams (i.e., 730, 731 and 732)including a stream enriched in butene-2 732. In some cases, the butene-2732 is at least about 85%, about 90%, about 95%, about 99%, about 99.5%,about 99.9%, or about 99.95% pure. The butene-2 732 can go to themetathesis unit 702.

Additional butene-2 733 can be produced from the dimerization module 704(e.g., from ethylene). The additional butene-2 733 can be used directlyin the metathesis reactor 702 in some cases. However, as shown here, theadditional butene-2 can be recycled to the fractionation train (e.g., tothe de-ethanizer 716) to enrich the concentration of butene-2 prior tometathesis. In some cases, the C4 mix product from the dimerizationreactor is sent to the debutanizer since the dimerization reactoreffluent may comprise C4 components. Also, the product stream 733 can bea mix of butenes (butene-2, butene-2, n-butenes, iso-butenes) or can bea pure butene-2 rich stream.

The metathesis unit can produce a propylene stream 734 that can beutilized directly or enriched (e.g., to polymer grade propylene) byrecycling the dilute propylene stream 734 to the fractionation train(e.g., to the de-ethanizer 716).

The process can produce a number of additional streams that can beutilized directly or recycled in the process, such as an ethane stream735 coming from the C₂ splitter that can be recycled to the catalyst bed709 and/or ethane conversion section 710 of the OCM reactor 708.

In some cases, the C₂ compounds are not split into enriched ethylene orenriched ethane streams. With reference to FIG. 7B, the de-ethanizeroverhead 719 can be used in the metathesis module 702, in thedimerization module 704, and/or can be recycled to the OCM reactor 708directly (e.g., without first being separated in a C₂ splitter). In somecases, the C₂ stream 719 can go through a hydrogenation unit 720 (e.g.,that hydrogenates acetylene) to produce a hydrogenated C₂ stream 740,which hydrogenated C₂ stream 740 can be used in the metathesis module702, in the dimerization module 704. In some cases, the hydrogenated C₂stream 740 can contain at least about 5%, about 10%, about 15%, about20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%,about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about85%, about 90%, about 95%, or more compounds other than ethylene.

FIG. 8 shows an example of an integrated plant having OCM 800,dimerization 802 and metathesis 804. The C3 product 806 can be used forpolypropylene production. The polymer grade ethylene stream 808 can berouted to the dimerization and the metathesis unit. The dimerizationeffluent 810, which may comprise predominantly C4s stream can be sent tothe debutanizer 812. The mix butenes rich debutanizer overhead 814 canbe routed to the metathesis reactor 804 via a feed treater 816 that canremove any potential poisons for the metathesis catalysts. Themetathesis reactor effluent 818 can comprise propylene, some unreactedC4s and ethylene. The metathesis effluent can be routed to thede-ethanizer 820, the de-ethanizer overhead can be sent to the C2splitter 822 for ethylene recovery. The de-ethanizer bottoms can berouted to the de-propanizer 824, the de-propanizer overhead 806 cancontain greater than about 95% propylene. In some cases, a C3 splitter(not shown) can be used to further purify the C3 overhead to polymergrade propylene. In some cases, a C3 splitter can be installed in thesystem to produce high purity polymer grade propylene. A de-methanizer826 can recover non-reacted methane from the OCM product.

Mixing Devices, Systems and Methods

Recognized herein is the need for systems and methods for convertingmethane to higher chain hydrocarbons, such as hydrocarbon compounds withtwo or more carbon atoms (also “C₂₊ compounds” herein), in an efficientand/or commercially viable process. An oxidative coupling of methane(“OCM”) reaction is a process by which methane can form one or more C₂₊compounds.

In an aspect of the present disclosure, pre-conditioning of OCM reactantstreams may be achieved by mixing using mixer devices, systems andmethods for OCM processes. Such devices or systems can (i) mix themethane-containing and oxygen-containing streams with the requireddegrees of uniformity in terms of temperature, composition and velocity;and/or (ii) mix the methane-containing and oxygen-containing streamssubstantially completely, rapidly and efficiently in order to minimizethe residence time of the heated mixed gases before they can becontacted with and reacted in the catalyst bed, which may be less than,or substantially less than the amount of time for autoignition of themixed heated gases to occur.

Required composition uniformity can be such that the deviation of themost oxygen-rich and oxygen-poor post-mixing areas in terms of CH₄/O₂ratio is less than or equal to about 50%, 40%, 30%, 20%, 15%, 10%, 5%,4%, 3%, 2%, 1%, or less, as compared to a perfectly mixed stream.Required temperature uniformity can be such that the deviation of thehottest and coldest post-mixing zones from the temperature of theideally mixed stream is less than or equal to about 30° C., 20° C., 10°C., 5° C., or less. Required velocity uniformity can be such that thedeviation in flow of the post-mixing areas with the largest and smallestflow from the flow of the ideally mixed stream is less than or equal toabout 50%, 40%, 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1%, or less. Anylarger deviations of these variables from the average may cause thecatalytic bed located downstream of the mixer to perform with a reducedefficiency. Mixers of the present disclosure can aid in achieving adesired degree of compositional, pressure, temperature and/or flowuniformity in a time period lower than the auto-ignition delay time,such as within a time period from about 5 milliseconds (ms) to 200 msand/or a range of flow rates from about 1 Million standard cubic feetper day (MMSCFD) to 2,000 MMSCFD. In some cases, the auto-ignition delaytime is from about 10 milliseconds (ms) to 1000 ms, or 20 ms to 500 ms,at a pressure from about 1 bar (absolute) and 100 bars, or 1 bar to 30bars, and a temperature from about 300° C. to 900° C., or 400° C. and750° C.

If any portion of the mixed stream is allowed to spend longer than theauto-ignition delay time in the mixing zone before coming in contactwith a catalyst in the OCM reactor, this particular portion canauto-ignite and propagate combustion throughout the entire stream. Insome cases, 100% of the stream spends less than the auto-ignition time,which may require the mixer to be characterized by a substantiallynarrow distribution of residence times and the absence of a right tailin the distribution curve beyond the auto-ignition threshold. Such amixer can provide a non-symmetric distribution of residence times.

An aspect of the present disclosure provides an oxidative coupling ofmethane (OCM) process comprising a mixing member or device (or mixer) influid communication with an OCM reactor. The mixer is configured to mixa stream comprising methane and a stream comprising oxygen to yield astream comprising methane and oxygen, which is subsequently directed tothe OCM reactor to yield products comprising hydrocarbon compounds. Thehydrocarbon compounds can subsequently undergo separation into variousstreams, some of which can be recycled to the mixer and/or the OCMreactor.

The hydrocarbon compounds can include compounds with two or more carbonatoms (C₂₊ compounds). The hydrocarbon compounds can include C₂₊compounds at a concentration (e.g., mole % or volume %) of at leastabout 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, ormore. In some situations, the hydrocarbon compounds substantially orexclusively include C₂₊ compounds, such as, for example, C₂₊ compoundsat a concentration of least about 60%, 70%, 80%, 90%, 95%, 99%, 99.9%,or more.

Mixing can be employed in a mixer fluidically coupled to an OCM reactor.The mixer can be integrated with the OCM reactor, or be a standaloneunit. In some examples, the mixer is upstream of the OCM reactor. Inother examples, the mixer is at least partly or substantially integratedwith the OCM reactor. For example, the mixer can be at least partly orsubstantially immersed in a reactor bed of the OCM reactor. The reactorbed can be a fluidized bed.

Systems and methods of the present disclosure can maximize theefficiency of an OCM reaction and reduce, if not eliminate, undesiredreactions.

Fluid properties can be selected such that methane and an oxidizingagent (e.g., O₂) do not auto-ignite at a location that is before thecatalyst of the OCM reactor. For instance, a stream comprising methaneand oxygen can have a composition that is selected such that at most 5%,4%, 3%, 2%, 1%, 0.1%, 0.01%, or less of the oxygen in the mixed gasstream auto-ignites. The fluid properties include the period of time inwhich methane is in contact with oxygen (or another oxidizing agent).The residence time can be minimized so as to preclude auto-ignition. Insome cases, the stream comprising methane and oxygen can have asubstantially non-symmetric distribution of residence (or delay) timesalong a direction of flow of said third stream. The residence (or delay)time is the period in which a stream comprising methane and oxygen doesnot auto-ignite. In some examples, the distribution of residence timesis skewed towards shorter residence times, such as from about 5 ms to 50ms. Auto-ignition delay time may be primarily a function of temperatureand pressure and, secondarily, of composition. In some cases, the higherthe pressure or the temperature, the shorter the auto-ignition delaytime. Similarly, the closer the composition to the stoichiometryrequired for combustion, the shorter the auto-ignition delay time.Diagrams based on empirical data and thermodynamic correlations may beused to determine i) the auto-ignition region (i.e., the thresholdvalues of temperature, pressure and composition above or below whichauto-ignition may occur); and ii) the auto-ignition delay time insidethe auto-ignition region. Once the auto-ignition delay time isdetermined for the desired or otherwise predetermined operatingconditions, the mixer may be designed such that 100% of the mixed streamspends less than the auto-ignition time in the mixer itself prior tocontacting the OCM catalyst.

During mixing, flow separation may cause a portion of the flow to spenda substantially long period of time in a limited region due to eitherthe gas continuously recirculating in that region or being stagnant. Insome cases, flow separation causes this portion of the flow to spendmore time than the auto-ignition time prior to contact with thecatalyst, thus leading to auto-ignition and propagation of thecombustion to the adjacent regions, and eventually, to the entirestream.

Mixers of the present disclosure may be operated in a manner thatdrastically reduces, if not eliminates, flow separation. In somesituations, fluid properties (e.g., flow regimes) and/or mixergeometries are selected such that upon mixing a stream comprisingmethane with a stream comprising oxygen in a mixer flow separation doesnot occur between the mixer and the first gas stream, the second gasstream, and/or the third gas stream.

FIG. 9 shows an OCM system 900 comprising a mixer 901, an OCM reactor902 downstream of the mixer 901, and a separation unit 903 downstream ofthe OCM reactor 902. The arrows indicate the direction of fluid flow. Afirst fluid stream (“stream”) 904 comprising methane (CH₄) and a secondfluid stream 905 comprising oxygen (O₂) may be directed into the mixer901, where they may be mixed to form a third mixed gas stream 906 thatis directed into the OCM reactor 902. The second fluid stream 905 maycomprise CH₄ (e.g., natural gas) and O₂ mixed and maintained at atemperature below the auto-ignition temperature. In some cases, dilutingpure O₂ with methane may be desirable to enable relatively simplermaterial of construction for the mixer compared to situations in whichpure O₂ is used. In situations where pure O₂ is used, materials such asHastelloy X, Hastelloy G, Nimonic 90, and others should be used as theyare high temperature stable and resist metal ignition in oxygenenvironments. Such restrictions may be relaxed in the case of oxygendiluted with methane. In the OCM reactor 902, methane and oxygen mayreact in the presence of a catalyst provided within reactor 902, to formC₂₊ compounds, which are included in a fourth stream 907. The fourthstream 907 can include other species, such as non-C₂₊ impurities likeAr, H₂, CO, CO₂, H₂O, N₂, NO₂ and CH₄. The fourth stream 907 may then beoptionally directed to other unit operations for processing the outletgas stream 907, such as separation unit 903, used for separation of atleast some, all, or substantially all of the C₂₊ compounds from othercomponents in the fourth stream 907 to yield a fifth stream 908 and asixth stream 909. The fifth stream 908 can include C₂₊ compounds at aconcentration (e.g., mole % or volume %) that is at least about 10%,20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, or more, and the sixthstream 909 can include C₂₊ compounds at a concentration that is lessthan or equal to about 99%, 95%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%,10%, or less. The concentration of C₂₊ compounds in the fifth stream 908can be higher than the concentration of C₂₊ compounds in the sixthstream 909. The sixth stream 909 can include other species, such as Ar,H₂, CO, CO₂, H₂O, N₂, NO₂ and CH₄. The fifth stream and the sixth streamcan have different ethylene to ethane ratios. At least some, all orsubstantially all of CH₄ in the sixth stream 909 may optionally berecycled to the mixer 901 and/or the OCM reactor 902 in a seventh stream910. Ethane and/or propane can also be recycled. Propane, for example,can be recycled using a C₃ splitter. A separations unit can comprisereactive separations units, such as an ethylene-to-liquids reactor.Although illustrated in FIG. 9 as a separate unit operation, the mixercomponent of the system may be integrated into one or more unitoperations of an overall OCM process system. For example, in some cases,mixer 901 is an integrated portion of reactor 902, positionedimmediately adjacent to the catalyst bed within the reactor 902, so thatthat the mixed gas stream 906 may be more rapidly introduced to thereactor's catalyst bed, in order to minimize the residence time of mixedstream 906.

Methane in the first fluid stream 904 can be provided from any of avariety of methane sources, including, e.g., a natural gas source (e.g.,natural gas reservoir) or other petrochemical source, or in some casesrecycled from product streams. Methane in the first fluid stream may beprovided from an upstream non-OCM process.

The product stream 908 can be directed to one or more storage units,such as C₂₊ storage. In some cases, the product stream can be directedto a non-OCM process.

Fluid properties (e.g., flow regimes) may be selected such that optimummixing is achieved. Fluid properties can be selected from one or more offlow rate, temperature, pressure, and concentration. Fluid propertiescan be selected to achieve a given (i) temperature variation in thethird stream 906, (ii) variation of concentration of methane to theconcentration of oxygen in the third stream 906, and/or (iii) variationof the flow rate of the third stream 906. Any one, two or all three of(i)-(iii) can be selected. In some cases, the temperature variation ofthe third stream 906 is less than or equal to about 100° C., 90° C., 80°C., 70° C., 60° C., 50° C., 40° C., 30° C., 20° C., 10° C., 5° C., 1°C., or less. The variation of the concentration of methane to theconcentration of oxygen (CH₄/O₂) in the third stream 906 can be lessthan about 50%, 40%, 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1%, or lesscompared to a perfectly mixed (or ideal) stream. The variation of theflow rate of the third stream 906 can be less than about 50%, 40%, 30%,20%, 15%, 10%, 5%, 4%, 3%, 2%, 1%, or less. Such variations can be ascompared to a perfectly mixed or thermally equilibrated stream and maybe taken along a direction that is orthogonal to the direction of flow.Variations can be measured at the exit plane of 906, for example.

The mixer 901 can mix the first stream 904 and the second stream 905 togenerate a stream characterized by uniform or substantially uniformcomposition, temperature, pressure and velocity profiles across a crosssection of a mixing zone of the mixer 901 or reactor 902 (e.g., along adirection that is orthogonal to the direction of flow). Uniformity canbe described in terms of deviation of the extremes from an averageprofile. For example, if the various streams possess differenttemperatures, the resulting profile of the mixed stream can show amaximum deviation of +/−1 to 20° C. between the hottest and coldestareas compared to the ideal (e.g., perfectly mixed) stream. Similarly,if the various streams possess different compositions, the resultingprofile of the mixed stream may show a maximum deviation of +/−0.1 to 20mole % of all reacting compounds compared to the composition of theideal stream. Similar metrics can be used for velocity and pressureprofiles.

In some cases, the system 900 can include at least about 1, 2, 3, 4, 5,6, 7, 8, 9, or 10 separation units. For example, the system 900 mayinclude one separation unit 903. The separation unit 903 can be, forexample, a distillation column, scrubber, or absorber. In cases wherethe system 900 includes multiple separation units 903, the separationunits 903 can be in series and/or in parallel.

The system 900 can include any number of mixers and OCM reactors. Thesystem 900 can include at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10mixers 901. The system 900 can include at least about 1, 2, 3, 4, 5, 6,7, 8, 9, or 10 reactors 902. The mixers 901 can be in series and/or inparallel. The reactors 902 can be in series and/or in parallel.

Although described for illustration of preferred aspects as gas streamspassing into, through and out of the reactor systems in FIG. 9, it willbe appreciated that the streams 904, 905, 906, 907, 908, 909 and 910 canbe gaseous streams, liquid streams, or a combination of gaseous andliquid streams. In some examples, the streams 904 and 905 are gaseousstreams, and the stream 908 and 909 are liquid streams. In someexamples, the streams 904, 905, and 909 are gaseous streams, and thestream 908 is a liquid stream.

In some cases, the system 900 includes multiple OCM reactors 902. TheOCM reactors 902 can be the same, similar or dissimilar reactors orreactor types arranged in series or parallel processing trains.

The OCM reactor 902 can include any vessel, device, system or structurecapable of converting at least a portion of the third stream 906 intoone or more C₂₊ compounds using an OCM process. The OCM reactor 902 caninclude a fixed bed reactor where the combined methane/oxygen gasmixture is passed through a structured bed, a fluidized bed reactorwhere the combined methane/oxygen mixture is used to fluidize a solidcatalyst bed, and/or a membrane type reactor where the combinedmethane/oxygen mixture passes through an inorganic catalytic membrane.

The OCM reactor 902 can include a catalyst that facilitates an OCMprocess. The catalyst may include a compound including at least one ofan alkali metal, an alkaline earth metal, a transition metal, and arare-earth metal. The catalyst may be in the form of a honeycomb, packedbed, or fluidized bed.

Although other OCM catalysts can be disposed in at least a portion ofthe OCM reactors 902, in some cases, at least a portion of the OCMcatalyst in at least a portion of the OCM reactor 902 can include one ormore OCM catalysts and/or nanostructure-based OCM catalyst compositions,forms and formulations described in, for example, U.S. PatentPublication Nos. 2012/0041246, 2013/0023709, 2013/0158322, 2013/0165728,and 2014/0274671, each of which is entirely incorporated herein byreference. Using one or more nanostructure-based OCM catalysts withinthe OCM reactor 902, the selectivity of the catalyst in convertingmethane to desirable C₂₊ compounds can be about 10% or greater; about20% or greater; about 30% or greater; about 40% or greater; about 50% orgreater; about 60% or greater; about 65% or greater; about 70% orgreater; about 75% or greater; about 80% or greater; or about 90% orgreater.

In the OCM reactor 902, methane and O₂ are converted to C₂₊ compoundsthrough an OCM reaction. The OCM reaction (e.g., 2CH₄+O₂→C₂H₄+2H₂O) maybe exothermic (ΔH=−67 kcals/mole) and may require substantially hightemperatures (e.g., temperature greater than 700° C.). As a consequence,the OCM reactor 902 can be sized, configured, and/or selected based uponthe need to dissipate the heat generated by the OCM reaction. In somecases, multiple, tubular, fixed bed reactors can be arranged in parallelto facilitate heat removal. At least a portion of the heat generatedwithin the OCM reactor 902 can be recovered, for example the heat can beused to generate high temperature and/or pressure steam. Whereco-located with processes requiring a heat input, at least a portion ofthe heat generated within the OCM reactor 902 may be transferred, forexample, using a heat transfer fluid, to the co-located processes. Whereno additional use exists for the heat generated within the OCM reactor902, the heat can be released to the environment, for example, using acooling tower or similar evaporative cooling device. OCM reactor systemsuseful in the context of the present invention may include thosedescribed in, for example, U.S. Patent Publication Nos. 2014/0107385 and2015/0152025, each of which is incorporated herein by reference in itsentirety for all purposes.

As described above, in certain aspects, a mixer device or system can beprovided coupled to or integrated with an OCM reactor or reactor system.Such mixers are described in greater detail below.

In some cases, two or more different reactant streams are mixed rapidlyand sufficiently for carrying out a reaction involving the two or morestreams. In some cases, mixing may be substantially completely within arapid timeframe within the mixer systems and devices described herein.

In some cases, two or more gaseous streams can be mixed in a mixerwithin a narrow window of time targeted to be less than the time inwhich autoignition may occur at the temperatures and pressures of themixed gas streams. Such narrow window of time can be selected such thatthe streams are mixed before any OCM reaction has commenced. In somecases, the mixing time is no longer than the maximum residence timebefore auto-ignition occurs. The mixing time can be less than or equalto about 99%, 95%, 90%, 80%, 70%, 60%, 50% or less of the maximumresidence time. Each and all portions of the mixed stream can spendnearly the requisite amount of time in a mixing zone of a mixer orreactor that is configured to effect mixing. If the reacting mixturespends more time, then undesired reactions, sometimes irreversible, maytake place, which may generate undesired products and possibly impede orprevent the formation of the desired products. Such undesired reactionsmay generate a greater proportion of non-C₂₊ impurities than C₂₊compounds, which may not be desirable.

In some situations, in order for the optimal residence time to beachieved by each portion of the mixing stream, the distribution of theresidence times in the mixing zone can be substantially narrow so as toreduce the possibility for even a small portion of the stream to spendless or more than the allowed time in the mixing area. Such phenomenoncan occur if recirculation and/or stagnant areas are formed due to thedesign of the mixer itself. For example, if the mixing device is aperforated cylinder located in the mainstream of the larger gaseousstream, the cylinder itself can produce significant recirculation zonesin the areas immediately downstream, thus generating a wide right tailin the statistical distribution of residence times. Systems and methodsof the present disclosure can advantageously avoid such problems.

The present disclosure provides systems and methods for mixing reactantspecies (e.g., methane and O₂) prior to or during reaction to form C₂₊compounds, such as by an OCM reaction. In some examples, i) two or moregaseous streams may be mixed together within a certain time frame andwith a given (e.g., minimum) degree of uniformity, and/or ii) theresulting mixed stream may afford a limited overall residence time and anarrow distribution of residence times before operating conditions ofthe stream are significantly affected by undesired chemical reactions.Prior to or during mixing, reactant species may be preheated.

A mixer can be integrated with an OCM reactor or separate from the OCMreactor, such as a standalone mixer. FIG. 10 shows an example OCM system1000 comprising a methane stream 1001 and an air stream (comprising O₂)1002 that are each directed through heat exchangers 1003 and 1004, whereeach of the streams 1001 and 1002 can be preheated. Next, the streams1001 and 1002 may be directed to a mixer 1005 comprising a plurality ofmixing nozzles 1006. The nozzles 1006 can be in two-dimensional array orin concentric circles, for example. The nozzles can each have the shapeof an airfoil, as described elsewhere herein. Void space 1007 betweenthe nozzles 1006 can be filled with a packing material (e.g., silica) toaid in preventing recirculation of the mixed gas.

The system 1000 may further comprise a catalyst bed 1008 downstream ofthe mixer 1005. The catalyst bed 1008 can include an OCM catalyst, asdescribed elsewhere herein. A void space 1009 between the mixer 1005 andcatalyst bed 1008 can be unfilled, or filled with an inert medium, suchas, for example, aluminum oxide (e.g., alumina) or silicon oxide (e.g.,silica) beads. In some cases, the void space can be filled with amaterial that increases the auto ignition delay time (AIDT), for exampleby changing the heat capacity of the media and/or interacting with theinitial stage of combustion chemistry by scavenging highly reactivespecies that can act as combustion initiators. Suitable materials caninclude zirconia beads, ceramic foams, metal foams, metal or ceramichoneycomb structures, or combinations thereof. The use of materials thatincrease the AIDT can be advantageous at elevated pressures (e.g., aboveabout 3, 5, 10, 15, 20, 25, 30, 35, or 40 barg). The system 1000 caninclude a reactor liner 1010 that can insulate the system 1000 from theexternal environment. The liner 1010 can thermally insulate the mixer1005 and catalyst bed 1008 from the external environment.

In each nozzle 1006 of the mixer 1005, methane and air (includingoxygen) can be mixed to form a mixed stream that is directed to thecatalyst bed 1008. In the catalyst bed 1008, methane and oxygen matreact to form C₂₊ compounds in an OCM process. The C₂₊ compounds alongwith other compounds, such as unreacted methane and oxygen, may bedirected out of the system 1000 in a product stream 1011.

In some cases, mixers include one or more airfoils. FIGS. 11A and 11Bshow an example OCM system 1100 comprising a mixer (or injector) 1101and a gas distribution manifold 1102 adjacent to the mixer 1101. FIG.11B schematically illustrates a cross-section of the system 1100, takenalong line 11B-11B in FIG. 11A. The mixer 1101 may comprise a pluralityof ribs 1103 that are airfoils. An upstream portion of each of the ribs1103 may have a larger cross-section than a downstream portion of eachof the ribs 1103. The ribs 1103 may or may not be hollow.

In some cases, a mixer is capable of mixing a first gas (e.g., CH₄) anda second gas (e.g., O₂) within about 1,000 milliseconds (ms), 900 ms,800 ms, 700 ms, 600 ms, 500 ms, 400 ms, 300 ms, 200 ms, 100 ms, 50 ms,10 ms, or less. The mixer can include a plurality of manifolds, such asairfoil-shaped manifolds, distributed across a fluid flow path.

In FIGS. 11A and 11B, a first fluid stream may be directed into the gasdistribution manifold 1102 at a first inlet 1104. A second fluid streammay be directed into the mixer 1101 at a second inlet 1105 (along thedirection of the arrows (i.e., upstream do downstream), at which pointthe second fluid stream may be directed to along a fluid flow path 1106to the ribs 1103. The fluid flow path 1106 can be a chamber that is influid communication with the inlet 1105 and the ribs 1103. In someexamples, the first fluid stream comprises a hydrocarbon (e.g., methane)and the second fluid stream comprises an oxidizing agent. In some cases,the second fluid stream is air and the oxidizing agent is O₂.

The system 1100 may further comprise an OCM reactor 1107 downstream ofthe mixer 1101. The ribs 1103 are situated along a fluid flow path thatleads from the inlet 1104 to the OCM reactor 1107. During use, the firstfluid stream may enter the system 1100 at the inlet 1104 and may bedirected to the gas distribution manifold 1102. The second fluid streammay enter the system 1100 at the inlet 1105 and may be directed alongthe fluid flow path 1106 to the ribs 1103. As the second fluid stream isdirected along the fluid flow path, heat from the OCM reactor 1107 canheat the second fluid stream. The heated fluid stream may enter the ribs1103 and may be directed out of the ribs to mix with the first fluidstream that is directed towards the OCM reactor 1107 from the gasdistribution manifold 1102.

The mixer 1101 can be close coupled with the OCM reactor 1107. In somecases, the OCM reactor 1107 includes a catalyst. The catalyst may beincluded in a space between the ribs 1103. The OCM reactor 1107 can havevarious shapes and sizes. The OCM reactor 1107 can have a cross-sectionthat is circular, oval, triangular, square, rectangular, pentagonal,hexagonal or any partial shape and/or combination thereof. In anexample, the OCM reactor 1107 is cylindrical in shape. In some examples,the OCM reactor 1107 has a diameter between about 1 foot and 100 feet,or 5 feet and 50 feet, or 10 feet and 20 feet. In an example, the OCMreactor 1107 has a diameter that is about 12 feet.

The OCM reactor 1107 can include a liner 1108 that can be formed of arefractory material. Examples of refractory materials include the oxidesof aluminum (e.g., alumina), silicon (e.g., silica), zirconium (e.g.,zirconia) and magnesium (e.g., magnesia), calcium (e.g., lime) andcombinations thereof. Other examples of refractory materials includebinary compounds, such as tungsten carbide, boron nitride, siliconcarbide or hafnium carbide, and ternary compounds, such as tantalumhafnium carbide. Refractory material can be coated and/or doped withrare earth elements or oxides, or other basic alkaline earth and/oralkali metals. This may aid in preventing coking. OCM catalyst nanowiresmay also be used to coat refractory material to prevent coking. Theliner 1108 can have a thickness from about 0.5 inches and 24 inches, or1 inch and 12 inches, or 3 inches and 9 inches. In an example, the liner1108 has a thickness of about 6 inches.

The inlets 1104 and 1105 can have various shapes and sizes. The inlet1105 can have cross-section that is circular, oval, triangular, square,rectangular, pentagonal, hexagonal or any partial shape and/orcombination thereof. In some examples, the inlet 1104 has a diameterbetween about 10 inches and 100 inches, or 20 inches and 80 inches, or40 inches and 60 inches. In an example, the inlet 1104 has a diameterthat is about 56 inches. In some examples, the inlet 1105 has a diameterbetween about 1 inch and 50 inches, or 10 inches and 30 inches, or 15inches and 20 inches. In an example, the inlet 1105 has a diameter thatis about 18 inches.

Each of the ribs 1103 can be an airfoil mixer that is configured tobring the second fluid stream in contact with the first fluid stream.This can provide for uniform mixing. Each of the ribs 1103 can includeone or more openings that are in fluid communication with a fluid flowpath leading from the inlet 1104 to the OCM reactor 1107. In someexamples, each of the ribs 1103 has an opening on a top or bottomportion of a rib (with respect to the plane of the figure) and/or onopposing side portions—i.e., along a direction that is orthogonal to thedirection of fluid flow from the inlet 1104 to the OCM reactor 1107. Byintroducing the second fluid stream to the first fluid stream prior tothe OCM reactor 1107, the ribs can enable mixing of the first and secondfluid streams prior to an OCM reaction in the OCM reactor 1107.

In some cases, the point along a given rib 1103 at which the secondfluid stream is introduced to the first fluid stream, as well as thefluid properties of the respective streams (e.g., pressure, flow rateand/or temperature), is selected such that the auto-ignition (e.g.,automatic combustion or partial combustion of methane) prior to the OCMreactor 1107 can be minimized, if not eliminated. This can help ensurethat reaction between a hydrocarbon (e.g., methane) and an oxidizingagent (e.g., oxygen) occurs in the OCM reactor 1107 to yield C₂₊compounds, and helps reduce (e.g., by at least 50%, 60%, 70%, 805%, 90%,or more), if not eliminate, unwanted reactions, such as the partial orcomplete combustion of the hydrocarbon. In some examples, the secondstream is introduced to the first stream at the top of each of the ribs1103.

A rib can be a blade that is in the shape of an airfoil. FIG. 12 showsan example blade 1201 that may be employed for use as a rib. In someexamples, the blade can have a width (the widest portion, ‘W’) fromabout 0.5 inches to 10 inches, and a length from about 0.5 ft. to 10 ft.The blade 1201 can be part of a mixer upstream of an OCM reactor. Themixer can be integrated with the OCM reactor. The mixer and OCM reactorcan be integrated with a heat exchanger (see below). During operation ofan OCM system having the blade 1201, a first fluid stream may bedirected along a fluid flow path 1202. The first fluid stream caninclude a hydrocarbon, such as methane. A second fluid stream 1203 maybe directed out of the blade 1201 through openings 1204 on opposingsides of the surfaces of the blade 1201. The openings 1204 can be holesor slits, for example. The second fluid stream 1203 can include anoxidizing agent, such as oxygen (O₂). In some cases, the second fluidstream 1203 includes air. The second fluid stream can include a mixtureof oxygen and methane.

The openings 1204 can be on the sides of the blade 1201. As analternative or in addition to, the openings 1204 can be on a top and/orbottom portion of the blade (with respect to the plane of the figure).The blade 1201 can have at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,20, 30, 40, 50, or 100 openings, which can have various sizes andconfigurations. For example, the openings 1204 can be holes or slits.The openings can be disposed side-by-side along the length of the blade1201 (i.e., along an axis orthogonal to the width of the blade (‘W’) andin the plane of the figure), or side by side along a thickness of theblade 1201 (i.e., along an axis orthogonal to the width of the blade andorthogonal to the plane of the figure).

The mixer can provide rapid and complete mixing of two or more gasstreams. Additionally, the airfoil shape can help minimize, if noteliminate, stagnant or re-circulation zones in a mixing zone downstreamof the mixer. This may allow for every portion of the mixed stream tospend the same amount of time within the mixing zone, thus leading to avery narrow and controlled distribution of the residence times in themixing zone itself.

Pre-Heating Devices, Systems and Methods

Another aspect of the present disclosures provides heating devices,systems and methods. Such devices, systems and methods may be employedfor use in pre-heating reactant streams prior to an OCM reaction.Pre-heating devices, systems and methods of the present disclosure canbe used separately or in conjunction with other pre-conditioningapproaches of the present disclosure, such as mixing. For example, apre-heater can be integrated with a mixer. As another example, apre-heater can be separate from a mixer and situated upstream ordownstream of the mixer but situated prior to an OCM reactor.

In some cases, streams comprising an oxidizing agent (e.g., O₂, whichmay be provided by way of air) and/or methane are heated by reactionheat prior to being mixed. This can advantageously reduce the amount ofreaction heat that is lost as waste heat, which can decrease the amountof energy that is used in external heat exchangers to pre-heat thestreams.

For example, an air stream or methane stream can be heated by heat froman OCM reactor. As another example, a mixed stream comprising air andmethane may be heated by heat from an OCM reactor. The air and/ormethane stream can be directed along a location that is in thermalcommunication with a catalyst bed to provide heat to the air and/ormethane stream prior to mixing or an OCM reaction to generate C₂₊compounds. In some examples, the air and/or methane stream are directedto a heat exchanger that is integrated with the OCM reactor, where atleast a portion of the heat from the OCM reaction is transferred to theair and/or methane stream.

In some cases, a system for performing an OCM reaction to generate C₂₊compounds comprises an OCM reactor comprising an OCM catalyst thatfacilitates the OCM reaction to generate the C₂₊ compounds, and aninjector comprising a fluid flow conduit that directs a first gas streamthrough at least a portion of the OCM reactor to one or more openingsthat are in fluid communication with the OCM reactor. The fluid flowconduit may be in thermal and/or fluidic communication with the OCMreactor, and the first gas stream comprises one of methane and anoxidizing agent. In some examples, the oxidizing agent includes oxygen(O₂). The system may further comprise a gas distribution manifoldcomprising one or more openings that are in fluid communication with theone or more openings of the injector and the OCM reactor. The gasdistribution manifold may direct a second gas stream into the OCMreactor. The second gas stream may comprise the methane and/or theoxidizing agent.

An OCM reactor can be integrated with a heat exchanger, which can enablereactant streams to be preheated by heat liberated from a reactor tooptimize a downstream reaction, such as an OCM reaction. For example, astream comprising an oxidizing agent (e.g., 02), such as an air stream,can be heated with a stream comprising a hydrocarbon stream (e.g.,methane) prior to mixing. The mixed stream can then be directed to theOCM reactor, as described above or elsewhere herein.

A mixture of methane and oxygen can be reactive above a giventemperature. The auto-ignition temperature of methane in air is about580° C. at atmospheric pressure. Under such conditions, bringing methanein contact with oxygen at such elevated temperature may lead topremature reaction, such as partial or complete combustion, leading topotentially undesirable products, such as CO and CO₂. However, in somecases, it may not be desirable to decrease the temperature of a methaneand/or O₂ stream (e.g., below the auto-ignition temperature) as this maydecrease the overall conversion in an OCM process.

The present disclosure provides various approaches for reducing theauto-ignition of methane. In some cases, the time that methane is incontact with O₂ is reduced while the temperature of the methane and/orO₂ streams is maintained at a requisite level to effect a given degreeof conversion. The light off temperature for an OCM reaction can be afunction of linear flow rate through the OCM reactor (e.g., catalystbed). Similarly, minimal inlet temperature under operating conditionsmay be affected by the linear flow rate though the OCM reactor.

In some cases, an inlet section is used to process a fraction of theinlet gas feed (e.g., less than 33%) at reduced local flow rate andinject the reaction product in a second section of the OCM reactor whereunreacted bypass feed will contact a hotter reacted product stream(e.g., stream containing C₂₊ compounds), such as in a counter flowfashion. The hotter product stream can be used to promote the OCMreaction by increasing the OCM reactor temperature relative to thereactor feed inlet. In some examples, an artificially created bypasschannel is provided through at least a portion of an OCM reactor, whichcan decrease the feed linear flow rate in the front end of the OCMreactor compared to the feed linear flow rate in the back of the OCMreactor.

OCM systems of the disclosure can be integrated with heat exchangers,which can enable heat liberated in an OCM reaction to be used to heat(or preheat) methane and/or an oxidizing agent (e.g., O, which may beprovided by air) prior to an OCM reaction.

Integrated heat exchangers of the disclosure may enable the creation andmaintenance of a hot spot within an OCM catalyst, allowing an OCMreactor to be operated with a reduced temperature inlet compared tocases in which an integrated heat exchanger is not used. In someimplementations, the inlet gas is heated to the necessary temperature bya heat exchanger, which enables the OCM reaction in a fixed bed reactor.This temperature can be between 300° C.-550° C. This approach may besensitive to the oxygen concentration in the feed and requiresubstantially short residence times from the heater to the catalyst bedto prevent combustion, such as via auto-ignition. The heat exchangercapital cost may also be an issue. For example, the inlet temperaturecan be about 350° C. for a fluidized bed reactor (in some cases withrelatively high reverse flow direction heat transfer), which can enableincreased conversion in an adiabatic bed as well as minimizing the riskof premature ignition, especially when using pure O₂ as the oxidizingagent in the OCM reaction.

In some cases, a heating element is lined externally with an OCMcatalyst (e.g., coated or a sleeve is placed over heater surface). Theheating element can have a relatively low heat transfer efficiency so asto maintain a high skin (or boundary layer) temperature of the OCMcatalyst that externally coats the heating element. As the inlet gaspasses adjacent to the heating element, gas near the surface of thecatalyst can be heated to a temperature that is at or near the skintemperature, which can initiate the OCM reaction and release heat thatcan mix with the bulk gas, uniformly heating the process gas stream. Theskin temperature of the OCM-catalyst lined heating element can besufficiently high so as to help ensure that the OCM reaction is highlyselective (e.g., from about 750° C. to about 900° C.) for a desirableproduct (e.g., C₂₊ compounds). In some cases, as the OCM reactionproceeds on the heating element surfaces, it produces heat thatincreases the inlet gas temperature as well as produces desirable OCMreaction products (e.g., C₂₊ compounds, water). This can be an approachto both reduce inlet heat exchanger capital costs as well as enable muchhigher single stage conversions, because the inlet O₂ (or otheroxidizing agent) concentration can be sufficiently high to heat theinlet gas from low temperatures (e.g., 25° C.-300° C.) to the desiredreactor inlet temperature (e.g., 400° C.-600° C.). For example, about10% conversion of methane at a C₂ selectivity approaching 60% may heatthe inlet gas from 200° C. to 500° C. An additional 10% conversion canbe attained in the fixed bed portion of the reactor, for example,resulting in a much higher single stage conversion. Heat exchangerslined with OCM catalysts of the present disclosure can take advantage ofthe substantially rapid OCM reaction kinetics at temperatures in excessof 750° C., which may only require a limited number of catalyst coatedheating elements to heat the inlet gas, while still maintaining asubstantially short residence times to prevent combustion prior to thecatalyst bed. The limited number of tubes and poor heat transfer to thegas stream may keep the heating duty of the inlet gas heat exchangerlow, and the exit gas from the reactor can potentially be used as theheating medium. In such a case, at least an additional heater may berequired to initiate the reaction.

Integrated heat exchangers of the present disclosure can be used totransfer heat to a gas stream undergoing a homogeneous endothermicreaction, such as alkane cracking into alkenes. For example, an OCMreactor may include a cracking unit downstream of a catalyst unitcomprising an OCM catalyst. The cracking unit can be heated using heatgenerated in the catalyst unit in an OCM reaction.

Reactors of the present disclosure can be operated or designed tooperate with reduced linear velocity. Reduced linear velocity operationcan promote feed pre-heating. Reduced linear velocity operation canreduce axial convective heat transfer. Reduced linear velocity operationcan move the peak bed temperature location toward the front end of thebed. Reaction heat can be used for stream preheating. Reduced linearvelocity operation can result in reduced oxygen consumption in lowselectivity regions. Reduced linear velocity operation can increasereaction selectivity across the reactor. A reactor can operate withreduced linear velocity in part of or in the entire reactor. Forexample, a reactor can comprise a low linear velocity region followed bya high linear velocity region. Linear velocity can be controlled betweenreactor regions by changing the reactor diameter or width. A reactor cancomprise an annular reactor, wherein a feed stream enters the centralregion and flows from the central region to the outer region.

The linear velocity can be any suitably low value, such as less than orequal to about 3 meters per second (m/s), about 2.5 m/s, about 2 m/s,about 1.5 m/s, about 1 m/s, about 0.5 m/s, about 0.4 m/s, about 0.3 m/s,about 0.2 m/s, about 0.1 m/s, about 0.05 m/s, about 0.01 m/s or less.

The present disclosure provides for tubular reactor systems. A tubularreactor can comprise a single stage. A tubular reactor can employ a heatremoval medium, such as molten salt. A heat removal medium can be usedfor heat removal from a reactor bed. A heat removal medium can be usedfor preheating feed streams. Tubular reactor systems can be used forreactions including but not limited to oxidative coupling of methane(OCM) and oxidative dehydrogenation of ethane (ODH). Temperature controlin a tubular reactor bed can be controlled by designing different bedproperties in segments. Such bed segmentation to the temperature profilecan be achieved by controlling the linear velocity of the reaction gas,for example by varying the tube diameter or by including non-reactivesleeves or inserts. Bed segmentation to control the temperature profilecan be achieved by controlling the thermal conductivity of the bed, forexample by controlling the catalyst form (e.g., shape, size, extrudates,rings, monoliths, foams) or by choice of catalyst support (e.g.,alumina, SiC, silica, magnesia). Bed segmentation to control thetemperature profile can be achieved by changing the thermal conductivityof the tube wall liner. Bed segmentation to control the temperatureprofile can be achieved by using multiple heat removal medium sectionswith varying levels of turbulence or temperatures.

In some cases, incomplete mixing of the methane source and the oxygensource can result in reduced performance of the OCM catalyst (e.g., dueto the formation of hot spots where oxygen concentration is relativelyhigher). In some cases, additional degrees of freedom with regard tomethane and oxygen mixing (e.g., temperature differences, spatialdifferences or frequency differences) can be manipulated to improve theperformance of the OCM reaction.

For example, the temperature of the methane source and the oxygen sourcecan be altered or adjusted independently to compensate for hot spotformation due to incomplete mixing. Having the inlet oxygen source(e.g., air) cooler than the methane source (e.g., natural gas), cancreate a self-correcting system where the mixture temperature isrelatively lower for portions of the mixture that are relatively higherin oxygen concentration. The somewhat lower inlet temperature can atleast partially compensate for the increased change in temperature(e.g., due to the relatively higher oxygen concentration resulting inadditional heat released in the OCM reaction).

Another effect of the relatively lower inlet mixture temperature forportions of the mixture that are relatively higher in oxygenconcentration is that the ignition of OCM is somewhat delayed, resultingin more radial mixing prior to initiation of the OCM reaction. Botheffects can have the desired outcome of reducing the occurrence of, andtemperature of hot spots. Hot spots can create increased flow resistancethrough porous media, shifting the flow profile within a catalyst bed.

In an aspect, the present disclosure provides a method for performing anoxidative coupling of methane (OCM) reaction. The method can compriseheating a first stream comprising methane (CH₄) to a first temperature,heating a second stream comprising oxygen (O₂) to a second temperature,and mixing the first stream and the second stream to produce a thirdstream. The second temperature may be lower than the first temperature.The third stream can be contacted with an OCM catalyst to perform an OCMreaction. In some cases, the first stream is natural gas and the secondstream is air.

In some instances, the first stream and second stream are mixed prior toperforming the OCM reaction. In some cases, the first stream and secondstream are imperfectly. Portions of the third stream that have arelatively higher concentration of O₂ can have a lower initialtemperature due to e.g., the second temperature is lower than the thirdtemperature, and/or a maximum temperature created in the OCM reaction isreduced relative to perfect mixing and/or the second temperature beingapproximately equal to the third temperature. In some cases, thelight-off temperature is reduced relative to perfect mixing and/or thesecond temperature being approximately equal to the third temperature.

In some cases, a difference between the first temperature and the secondtemperature is greater than or equal to about 20° C., 40° C., 60° C.,80° C., 100° C., 120° C., 140° C., 160° C., 180° C., 200° C., 240° C.,260° C., 280° C., 300° C., 350° C., 400° C., or more. In some cases, thedifference is between any of the two values described herein, forexample, from about 25° C. to about 200° C.

The desire to keep the methane source below a certain temperature tolimit coking can limit the practical temperature difference between theinput streams. Coking can be substantially reduced when the temperatureof natural gas is kept below about 550° C. for wet gas (e.g., comprisingat least about 1% C₂₊ compounds) and below about 600° C. for dry gas(e.g., comprising at most about 1% C₂₊ compounds).

While avoiding coking can provide a practical upper limit for themethane source temperature, the desired temperature of the mixture canprovide a practical lower limit for the temperature of the oxygensource. Also, the relative heat capacities of the methane source and theoxygen source can put constraints on the temperature difference that canbe achieved. Methane has about a 10-fold greater molecular heat capacitythan oxygen. The heat capacity of nitrogen is higher than oxygen, so insome cases, the use of air as the oxygen source can allow for a higherrelative temperature difference between the oxygen source and themethane source, as compared to the situations where pure or enriched O₂is used. In some cases, the heat capacity of the second stream isgreater than or equal to about 30%, 40%, 50%, 60%, 70%, or more of theheat capacity of the third stream.

Table 2 shows three example scenarios for differential temperaturemixing. The feed temperatures are shown in the upper portion of thetable. The temperatures of the mixtures (i.e., inlet temperatures absentthe heat of reaction) are shown in the middle portion of the table forperfect mixing and scenarios where a portion of the mixture isimperfectly mixed and contains relatively more or less air. The bottomthird of the table shows the inlet temperature difference that isachieved in the various scenarios (e.g., that can off-set any hot spotformation in the subsequent OCM reaction).

TABLE 2 Examples of Temperature Differences Scenario Scenario Scenario#1 #2 #3 Feed Stream Temperatures (° C.) CH₄ (50 kmol) 520 550 550 N₂(17 kmol, i.e., component of 520 380 260 Air) O₂ (4.5 kmol, component ofAir) 520 380 260 Final Mixture Temperatures (° C.) Perfect Mixing 520520.6 500.0 +10% Air 520 518.0 496.0 −10% Air 520 523.1 504.0 +20% Air520 515.6 492.0 −20% Air 520 525.7 508.8 Temperature Range (° C.) @ +/−10% Air 0 5.1 8.0 @ +/− 20% Air 0 10.1 16.8

In some cases, the methods described herein shift the position of thehot spot in the OCM reactor (e.g., shift it axially further from theinlet). In some cases, the methods described herein create “virtualbypass channels” where oxygen remains unreacted when initially contactedwith the OCM catalyst, to be available for reaction at a later portionof the OCM catalyst bed. Benefits of bypass channels are furtherexplained in U.S. Patent Publication No. 2015/0152025, which isincorporated herein by reference in its entirety. The virtual bypasschannel can achieve the same or a similar function to the physicalbypass, allowing some parts of the catalyst bed to be used as catalyticheating elements to condition a portion of the feed gas. This can resultin the ability to operate the reactor at a lower overall inlettemperature, enabling greater per pass conversion through the catalystbed and increasing yields of desirable products. This can also stabilizethe performance of the reactor and enable greater process fluctuationand turn down.

The present disclosure also provides systems and methods for injectingmethane and/or oxygen, or various concentrations or temperatures thereofinto different portions of the cross-section of an OCM reactor. Forexample, the mixing manifold for the O₂ source gas can be split in twoor more manifolds fed by different O₂ feed source gas streams atdifferent temperatures with different flows. This can result indifferent local CH₄ to O₂ ratios at the mixer exits, as well asdifferent local temperatures depending on the spatial distribution ofthe feed injectors and separately pre-heated O₂ feed stream. If the O₂source itself contains CH₄, the ratio of CH₄ and O₂ in each O₂ feedmanifold can be adjusted to provide additional control of the CH₄/O₂ratio spatial distribution exiting the mixer. For example, FIG. 13Ashows a reactor 1300, with a CH₄ feed 1301, and with O₂ feeds 1302 and1303 injected at different points along a direction perpendicular toflow. FIG. 13B shows graphs of the resulting variance in the local mixgas temperature (upper, gray) and the local mix gas percent oxygen(lower, black) in the x-dimension perpendicular to the flow dimension.The methane feed can also be split more coarsely and feed at differenttemperatures in different areas of the inlet of the O₂ feed distributorassembly. For example, FIG. 14A shows a reactor 1400 methane feeds 1401,1402, and 1403 in addition to oxygen feeds 1404 and 1405. FIG. 14B showsgraphs of the resulting variance in the local mix gas temperature(upper, gray) and the local mix gas percent oxygen (lower, black) in thex-dimension perpendicular to the flow dimension. As the methane feedcarries most of the heat capacity of the gas entering the reactor,heating a portion of the methane to a much higher temperature than theremainder of the methane feed can enable even larger swings in inlettemperature distribution. Some of the gas may enter the catalyst bed farbelow the light off temperature of the catalyst, provided that radialheat propagation is sufficient to progressively warm up the gas streamto a temperature above catalyst light off temperature.

Also provided herein is a method for performing an oxidative coupling ofmethane (OCM) reaction. The method can comprise heating a first streamcomprising oxygen (O₂) to a first temperature; dividing a second streamcomprising methane (CH₄) into at least two portions and heating each ofthe portions to a different temperature; injecting each of the portionsof the second stream into a different area of a mixer, which mixer mixesthe portions of CH₄ with the first stream; and contacting the mixturesproduced in (c) with an OCM catalyst to perform an OCM reaction. In somecases, the first stream is air and the second stream is natural gas.

In another aspect, provided herein is a method for performing anoxidative coupling of methane (OCM) reaction. The method can compriseheating a first stream comprising methane (CH₄) to a first temperature;dividing a second stream comprising oxygen (O₂) into at least twoportions and heating each of the portions to a different temperature;injecting each of the portions of the second stream into a differentarea of a mixer, which mixer mixes the portions of O₂ with the firststream; and contacting the mixtures produced in (c) with an OCM catalystto perform an OCM reaction. In some cases, the first stream is naturalgas and the second stream is air.

In some cases, the areas of the mixer into which each of the portions ofthe second stream comprising CH₄ and/or O₂ are injected are chosen toreduce a maximum temperature created in the OCM reaction (i.e., hotspot). In some cases, the areas of the mixer into which each of theportions of the second stream comprising CH₄ and/or O₂ are injected arechosen to bypass a portion of the O₂ further into the OCM catalyst. Inan example, some of the gas enters a section of the catalyst bed farbelow the light off temperature of the catalyst. The radial heatpropagation in the bed, as well as propagation of the catalystactivation within the catalyst bed, progressively warm up and reduce thevolume of this gas stream as it travels through the catalyst bed, untilthe last fraction of this gas reaches a temperature above the catalystlight off temperature. At this point, the O₂ contained in this streamwill be completely consumed by the OCM reaction. If cold gas in injectedalong a line in a plane with the catalyst entry face at the inlet of thereactor, the ignition front can be characterized by a wedge shape.

FIG. 15 shows an example of spatially differentiated mixing as describedherein. A top-view of the circumference 1500 into which methane isinjected in the mixer of FIG. 11A is shown (e.g., equivalent of 1104).Within the circumference 1500, there can be one or more areas 1501 thatare differentiated with respect to composition and/or inlet temperature.

The present disclosure also provides methods for mixing the oxygensource and the methane source at different frequencies (i.e.,alternately and repeatedly injecting the methane and oxygen into the OCMreactor or mixer). The alternative mixing can also be varied spatiallyover the area of the OCM reactor and have variation of temperature ofthe input streams, as described herein. In some cases, for a givenaverage condition set (e.g., composition, pressure and temperature) ofthe inlet oxygen and methane, local or time variations in conditions canbe used to manipulate the formation of hot spots and/or their maximumtemperature in order to improve OCM performance. In the case of temporaloscillation of feed composition and/or feed temperature, the heatcapacity of the catalyst particles can enable the transfer of energybetween the different streams. Such a transfer can potentially be moreeffective than long range heat propagation. This is similar in conceptto using fluid bed or flow reversal techniques with a decoupling ofsolid temperature where the gas temperature is never at a local thermalsteady state.

In another aspect, the present disclosure provides a method forperforming an oxidative coupling of methane (OCM) reaction. The methodcan comprise (a) providing a first stream comprising methane (CH₄) at afirst temperature; (b) providing a second stream comprising oxygen (O₂)at a second temperature; and (c) alternately (and in some casessequentially) injecting the first stream and the second stream into anOCM reactor which comprises an OCM catalyst to perform an OCM reaction.In some cases, the second temperature is less than the firsttemperature.

The first stream and the second stream can be alternated at a frequency.The frequency can be greater than or equal to about 0.01 Hertz (Hz),about 0.05 Hz, about 0.1 Hz, about 0.5 Hz, about 1 Hz, about 5 Hz, about10 Hz, about 50 Hz, about 100 Hz, about 500 Hz, or more. In some cases,the frequency is between about 0.1 and about 10 Hz. The frequency canalso be selected based on the relative heat capacity of the gas and thesolids to set a lower limit on the modulation frequency. An upper limiton the modulation can be set based on a multiple of mixer residencetime; for example, for a mixer residence time of 100 milliseconds (ms),pulses at a frequency of 10 Hz may not be very sharp by the time theyreach the catalyst face.

In some cases, the frequency is varied in response to a temperaturemeasured in the OCM reactor (e.g., where relatively less O₂ is injectedinto the OCM reactor when the temperature in the OCM reactor approachesa maximum temperature).

The alternating injection can be performed with piezo-electric injectors(e.g., using an array of piezo-electric injectors distributed over across section of the reactor), such as those used to inject liquid fuelsin gasoline or diesel engines. Piezo-electric injectors can enable veryprecise control of the time profile of the injection as well as of theamount of the injection. For example, using pulse trains of a fewmilliseconds, gas injections can be controlled to control oscillationsin the composition of the mixed gas stream over a wide frequency range.Piezo-electric injectors may be engineered with increased flowcapacities for low density streams to enable gas injection.

Methods for Improving Olefin Yield

An aspect of the present disclosure provides OCM systems and methods forincrease the concentration of alkenes (or olefins) in C₂₊ compoundsoutputted from an OCM reactor. This can advantageously provide C₂₊product stream that may be better suited for downstream uses, such asthe commercial production of polymeric materials, as well as greatercarbon efficiency of the overall process. In some embodiments, an OCMsystem provides improved alkene yield by alkane cracking in a catalystunit or cracking unit. Such in situ cracking of alkanes can provide aproduct stream with hydrocarbon distributions tailored for various enduses.

FIG. 16 shows an example OCM system 1600 comprising an OCM reactor 1601,a cracking unit 1602 downstream of the OCM reactor 1601, and at leastone separation unit 1603 downstream of the cracking unit 1602. The OCMreactor 1601 and cracking unit 1602 can be separate units or integratedas a single unit, as illustrated by the dashed box. The arrows indicatethe direction of fluid flow from one unit to another. During use, afirst fluid stream (“stream”) 1604 comprising methane (CH₄) and a secondfluid stream 1605 comprising an oxidizing agent (e.g., 02) can bedirected into the OCM reactor 1601, where they may react in the presenceof a catalyst provided within reactor 1602 to form C₂₊ compounds, whichare included in a third stream 1606. The third stream 1606 can includeother species, such as non-C₂₊ impurities like Ar, H₂, CO, CO₂, H₂O, N₂,NO₂ and CH₄. The third stream 1606 may comprise OCM products, which caninclude C₂₊ compounds and non-C₂₊ impurities.

Next, the third stream 1606 may be directed to the cracking unit 1602.In the cracking unit 1602, alkanes in the C₂₊ compounds can react toform C₂₊ compounds with unsaturated moieties, which are outputted fromthe cracking unit 1602 in a forth stream 1607, such as carbon-carbondouble bonds (e.g., ethylene and propylene). The fourth stream 1607 canthen be directed to other unit operations for processing gases in thefourth stream 1607, such as the separation unit 1603 used for separationof at least some, all, or substantially all of the C₂₊ compounds fromother components in the fourth stream 1607 to yield a fifth stream 1608and a sixth stream 1609. The streams 1608 and 1609 can each be directedto one or more storage units. The fifth stream 1608 can be directed toC₂₊ storage or a non-OCM process.

Methane in the first fluid stream 1604 can be provided from any of avariety of methane sources, including, e.g., a natural gas source (e.g.,natural gas reservoir) or other petrochemical source, or in some casesrecycled from product streams. Methane in the first fluid stream may beprovided from an upstream non-OCM process.

The fifth stream 1608 can include C₂₊ (e.g., olefins) compounds at aconcentration (e.g., mole % or volume %) that is at least about 10%,20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, or more. The sixthstream 1609 can include C₂₊ compounds at a concentration that is lessthan or equal to about 99%, 95%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%,10%, or less. The sixth stream 1609 can include methane at aconcentration of greater than or equal to about 10%, 20%, 30%, 40%, 50%,60%, 70%, 80%, 90%, 95%, 99%, or more. The concentration of C₂₊compounds in the fifth stream 1608 can be higher than the concentrationof C₂₊ compounds in the sixth stream 1609. The sixth stream 1609 caninclude other species, such as Ar, H₂, CO, CO₂, H₂O, N₂, NO₂ and CH₄. Atleast some, all or substantially all of CH₄ in the sixth stream 1609 mayoptionally be recycled to the OCM reactor 1601 and/or the cracking unit1602 in a seventh stream 1610. C₂ splitting can also be employed forethane recycle to the OCM reactor and/or the cracking unit.

The at least one separation unit 1603 can include a plurality ofseparation units, such as at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 20,30, 40, or 50 separation units, at least some of which can be in seriesand/or parallel. In some examples, the at least one separation unit 1603is a full separation train, in some cases including one or moredistillation columns, scrubbers, etc. The at least one separation unit1603 can include an olefin/alkane splitter and/or CO₂ separation unit.The seventh stream 1610 can include C1 (methane) recycle to the OCMreactor 1601 and/or the cracking unit 1602.

In some examples, at least about 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%,50%, 60%, 70%, 80%, 90%, or more of the non-C₂₊ components (e.g., CH₄and/or N₂) of the fourth stream 1607 can be separated by the separationunit 1603 and directed along the sixth stream 1609. This can provide afifth stream 1608 that has a higher concentration of C₂₊ compounds,including olefins and higher molecular weight alkanes.

The system 1600 can include any number of OCM reactors 1601 and crackingunits 1602. The system 1600 can include at least about 1, 2, 3, 4, 5, 6,7, 8, 9, 10, or more OCM reactors 1601. The OCM reactors 1601 can be thesame, similar or dissimilar reactors or reactor types arranged in seriesor parallel processing trains. The OCM reactors 1601 can be in seriesand/or in parallel. The system 1600 can include at least about 1, 2, 3,4, 5, 6, 7, 8, 9, 10, or more cracking units 1602. The cracking units1602 can be the same, similar or dissimilar reactors or reactor typesarranged in series or parallel processing trains. The cracking units1602 can be in series and/or in parallel. Alternatively, the reactor1601 can be used as a cracking unit by periodically changing the feed ofthe reactor between OCM feed to a C₂₊ alkane rich feed. In such a case,the heat capacity of a catalyst bed in the reactor 1601 can be used foralkane cracking.

The system 1600 can include at least about 1, 2, 3, 4, 5, 6, 7, 8, 9,10, or more separation units. In the illustrated example, the system1600 includes one separation unit 1603. The separation unit 1603 can be,for example, a distillation column, scrubber, or absorber. If the system1600 includes multiple separation units 1603, the separation units 1603can be in series and/or in parallel.

Although described for illustration of certain aspects as gas streamspassing into, through and out of the reactor systems in FIG. 16, it willbe appreciated that the streams 1604, 1605, 1606, 1607, 1608, 1609 and1610 can be gaseous streams, liquid streams, or a combination of gaseousand liquid streams. In some examples, the streams 1604 and 1605 aregaseous streams, and the stream 1608 and 1609 are liquid streams.

In some examples, the separation unit 1603 can include more than twoproduct streams. For example, olefins can be directed out of theseparation unit 1603 along an olefin stream and ethane and propane canbe directed out of the separation unit 1603 along another stream. Thesixth stream 1609 may be dedicated to methane.

The OCM reactor 1601 can include any vessel, device, system or structurecapable of converting at least a portion of the third stream 1606 intoone or more C₂₊ compounds using an OCM process. The OCM reactor 1601 caninclude an adiabatic fixed bed reactor where the combined methane/oxygengas mixture is passed through a structured bed that can include anactive temperature control component (e.g., molten salt cooling systemor the like), an isothermal tubular fixed bed reactor where the combinedmethane/oxygen gas mixture is passed through a structured bed, anadiabatic radial fixed bed reactor where the combined methane/oxygen gasmixture is passed through a structured bed, a fluidized bed reactorwhere the combined methane/oxygen mixture is used to fluidize a solidcatalyst bed, a honeycomb, and/or a membrane type reactor where thecombined methane/oxygen mixture passes through an inorganic catalyticmembrane. In some cases, a radial fixed bed reactor may be used as theheat loss in the collection volume is minimized when inward flow isused. The cracker section outer wall may be the diffuser of the OCMreactor.

The cracking unit 1602 can be a chamber or a plurality of chambers, suchas a plurality of vessels or pipes. The cracking unit 1602 can includeinlets for accepting compounds at various locations along the crackingunit 1602. The cracking unit 1602 can have a temperature profile acrossthe cracking unit 1602 and along a direction of fluid flow leading froman inlet of the cracking unit 1602 to an outlet of the cracking unit1602. In some examples, an upstream portion of the cracking unit 1602 ishotter than a downstream portion of the cracking unit 1602.

The system 1600 can include a mixer upstream of the OCM reactor 1601.The mixer can be employed for use in pre-conditioning OCM reactants,which can prevent the auto-ignition of the reactant gases prior to theOCM process in the OCM reactor 1601.

The cracking unit 1602 may be integrated into one or more unitoperations of an overall OCM process system. For instance, although theOCM reactor 1601 and cracking unit 1602 are illustrated in FIG. 16 asseparate unit operations, the cracking unit 1602 can be part of the OCMreactor 1601. In some cases, the cracking unit 1602 is positionedimmediately adjacent to the catalyst bed within the reactor 1601, sothat that the C₂₊ compounds may be more rapidly introduced to thecracking unit 1602. When integrating the OCM reactor 1601 with thecracking unit 1602, improved heat integration can be obtained by using aradial fixed bed reactor.

Various approaches can be employed to introduce alkanes to an OCMreactor integrated with a cracking unit. FIG. 17 shows an approach thatmay be employed. The figure shows an example OCM reactor comprising anOCM catalyst unit with a downstream cracking unit, and ethane andpropane injection locations. The catalyst unit can include a catalystbed. A hydrocarbon feed (“HC feed”) may direct a hydrocarbon (e.g.,methane) to the OCM reactor, and an air/O₂ stream may direct air/O₂ tothe OCM reactor. The hydrocarbon and air/O₂ streams can be directed to apre-conditioning unit of the OCM reactor, such as a mixer. Ethane andpropane can be provided from an external source, such as an NGLprocessing facility and/or as recycle from an OCM product stream. Thehydrocarbon, air/O₂, ethane and propane streams can be directed to heatexchangers to preheat the streams prior to introduction to the OCMreactor. In the figures, lengths L₁, L₂ and L₃ can be selected tooptimize ethane and propane cracking to desired or otherwisepredetermined products, which can be a function of gas temperature andresidence time. The ethane injection location is upstream of the propaneinjection location. In FIG. 17, ethane and propane are injected at thesame location (or co-injected).

During use, the hydrocarbon and air/O₂ directed into the OCM reactor mayreact to form OCM products that may be directed along ahydrocarbon-containing stream to the cracking unit and out of the OCMreactor. In the cracking unit, any alkanes in the hydrocarbon-containingstream, including alkanes introduced to the catalyst unit and/orcracking unit from an external source and any alkanes formed in thecatalyst unit, can be cracked to alkenes and directed out of the OCMreactor along the hydrocarbon-containing stream.

An aspect of the present disclosure provides mixers and methods ofmixing compounds (e.g., ethane and propane) into the cracking unit.Operation of the OCM process with ethane added to the cracking unit canbenefit from conditions whereby; (a) ethane is injected into anduniformly mixed with the OCM exhaust gas, and (b) the mixed gases areprovided sufficient residence time for conversion prior to thermalquenching. Thermal quenching can halt reactions that yield undesirablehydrocarbon constituents at the expense of ethylene. The mixing ofethane and OCM exhaust gas can be accomplished in a process that israpid and results in a uniformly blended mixture.

In some cases, high ethylene yields are obtained by providing forresidence times between ethane injection and thermal quenching ofgreater than or equal to about 5 milliseconds (ms), 10 ms, 20 ms, 30 ms,40 ms, at least about 50 ms, 60 ms, 70 ms, 80 ms, 90 ms, 100 ms, 120 ms,140 ms, 160 ms, 180 ms, 200 ms, 300 ms, or 400 ms. In some cases, theresidence time is less than or equal to about 400 ms, 300 ms, 200 ms,180 ms, 160 ms, 140 ms, 120 ms, 100 ms, 90 ms, 80 ms, 70 ms, 60 ms, 50ms, 40 ms, 30 ms, 20 ms, 10 ms, 5 ms, or less. In some cases, theresidence time is between any of the two values described above, forexample, between about 10 ms and 100 ms, between about 30 ms and about80 ms, or between about 50 ms and about 60 ms.

In some cases, the alkane (e.g., ethane or propane) is mixed with theOCM exhaust gas uniformly before exiting the mixer, upon exiting themixer, or prior to initiation of a cracking reaction. The alkane and OCMexhaust gas can be mixed such that the mixed gas has variations intemperature, alkane concentration, or flow rate that do not deviate morethan about 1%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 50%, 60%, or 80% fromthe average temperature, alkane concentration, or flow rate.

The mixers and mixing processes described herein can result in broadspectrums of mixture ratios. In some cases, the OCM exhaust gas entersthe system at a large end of a converging section in an axial direction.Ethane is injected into the converging section through a plurality ofports that can be directed to produce ethane jets having axial, radialand tangential velocity components. The ports can be substantiallydirected in tangential and radial directions. The converging section canbe connected to a duct of smaller diameter (e.g., the reactor). Thegeometry of the converging and reactor sections (diameters and lengths)can be selected to provide the desired residence times for reactions tooccur. In some cases, a heat exchanger is located downstream of andconnected to the reactor, which can be utilized to thermally quench thegas stream. The mixer can be made out of materials that can withstandhigh temperatures (e.g., about 800° C. to 1000° C., which can be thetemperature of the OCM exhaust gas). Examples of suitable materials areceramics such as alumina.

An aspect of the present disclosure provides OCM systems and methods forincreasing the concentration of alkenes (or olefins) in C₂₊ compoundsoutputted from an OCM reactor. An OCM system can provide improved alkeneyield by in situ alkane cracking in a post-bed section of a reactor(post-bed cracking). Such in situ cracking of alkanes can provide aproduct stream with hydrocarbon distributions tailored for various enduses. This can advantageously provide C₂₊ product stream that may bebetter suited for downstream uses, such as the commercial production ofpolymeric materials, as well as greater carbon efficiency of the overallprocess.

Post-bed cracking techniques can comprise control of temperature andresidence time. Temperature and residence time can be chosen to favorhigher ethylene concentration in the effluent from an OCM reactor.Post-bed cracking can be achieved using energy within the OCM effluent.Post-bed cracking can comprise cracking in the presence of OCM effluentsteam. Cracking in the presence of steam, such as OCM effluent steam,can provide a higher C₂ ratio. Systems and methods of the presentdisclosure can be modified by post-bed cracking (PBC) embodiments foundin U.S. patent application Ser. No. 14/553,795, which is incorporatedherein by reference in its entirety.

The OCM reaction can be performed in an adiabatic reactor, an isothermalreactor, a fluidized bed reactor, or any combination thereof. Adiabaticreactor systems can have many advantages including that they are simplein operation and design and generate useful heat (e.g., steam) for otherprocess steps. Also, the heat generated in the adiabatic system can beused to non-catalytically crack ethane (either created in the OCMreactor added to the reactor) to ethylene. As a result, the ethylene toethane ratio can be very high exiting the adiabatic reactor system(e.g., about 5%).

In adiabatic reactor systems, the OCM reaction may be limited by thetemperature difference between the light-off temperature at the lowerend (e.g., temperature at which the OCM reaction initiates for the OCMcatalyst) and a maximum temperature at the higher end (e.g., anypractical limit imposed by the OCM catalyst, feedstock or productstability). Since the heat of reaction may be retained in the productstream, this temperature difference limits the percentage methaneconversion and lower methane conversion can increase the number and sizeof equipment needed for separation and other processing steps followingthe OCM reactor.

There are alternative reactor design systems which can allow for higherconversion such as multi-stage adiabatic, fluidized bed and isothermalreactor systems. Isothermal reactor designs (e.g., tubular reactors)continuously remove the heat from the catalyst as it is generated,allowing for high C₂₊ selectivity and very high conversion. Onepotential downside of isothermal OCM reaction is that the reactoreffluent is typically much cooler than for adiabatic reaction andpost-bed cracking may not viable (for isothermal) without adding asignificant amount of heat.

The present inventors recognized a surprising synergy in combining anisothermal reactor with an adiabatic reactor for exothermic reactionssuch as OCM. The adiabatic and isothermal reactors may operate inparallel, with a portion of the excess heat and energy from theadiabatic reactor (before or after post bed cracking) being used toconvert ethane in the isothermal reactor effluent into ethylene.

Described herein is a reactor system with at least one adiabatic reactorand at least one isothermal reactor. The system can have at least about1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more isothermal and/or adiabaticreactors. The reactors may be configured such that heat can be exchangedbetween them. The excess power generated from the adiabatic reactor canbe fed as heat to the vapor space of the reactor outlet of a tubularreactor (without air or oxygen). This can result in cracking of theethane, increasing the ethylene to ethane ratio, and increasing theethylene concentration in the isothermal outlet. In some cases, theeffluent of the isothermal reactor is injected into the post-bedcracking region of the adiabatic reactor. In some cases, the effluent ofthe isothermal reactor is combined with the effluent of the isothermalreactor following post-bed cracking in the adiabatic reactor. In someinstances, excess ethane is injected into the system (e.g., into the PBCregion of the adiabatic reactor or into the combined reactor effluent).

With reference to FIG. 18, described herein is an example method forperforming an oxidative coupling of methane (OCM) reaction. The methodcan comprise inputting a first portion of methane (CH₄) 1800 and a firstportion of oxygen (O₂) 1802 into a first OCM reactor 1804, where thefirst OCM reactor is an adiabatic reactor. The method can include, inthe first OCM reactor, producing a first product stream 1806 comprisingC₂₊ products and liberating a first portion of heat, which first portionof heat increases the temperature of the first product stream. Themethod can include inputting a second portion of CH₄ 1808 and a secondportion of oxygen O₂ 1810 into a second OCM reactor 1812, where thesecond OCM reactor is an isothermal reactor. The method can include, inthe second OCM reactor, producing a second product stream 1814comprising C₂₊ products and liberating a second portion of heat, whichsecond portion of heat is removed from the second OCM reactor. In somecases, the method includes combining 1816 the second product stream withthe first product stream, whereby the first portion of heat convertsethane (C₂H₆) in the first and/or second product stream(s) into ethylene(C₂H₄).

In some cases, the method further comprises adding C₂H₆ to the firstproduct stream to convert the added C₂H₆ into C₂H₄. The C₂H₆ can beadded before 1818 or after 1820 combining the first product stream withthe second product stream. The first OCM reactor can have a reactionzone comprising an OCM catalyst 1822 and a post-bed cracking zone 1824.In some cases, the second reactor is a tubular reactor. In someinstances, the second reactor is a fluidized bed reactor.

A fluidized bed reactor can be used to pre-heat a methane feed (e.g.,natural gas) by running the methane feed in coils within the fluid bed.This can be advantageous relative to the use of a fired heater, as itcan be clean, can result in no additional emission heat, and can helpthe fluidized bed C₂ yield by removing heat. In this case, the ratio ofthe fluidized bed reactor capacity and the adiabatic reactor capacitycan be matched to properly pre-heat the methane feed.

The first portion of heat can increase the temperature of the firstproduct stream to at least about 650° C., at least about 700° C., atleast about 750° C., at least about 800° C., at least about 850° C., atleast about 900° C., or more.

Heat can be removed from the isothermal reactor such that thetemperature of the second product stream is less than or equal to about800° C., 750° C., 700° C., 650° C., 600° C., 550° C., 500° C., 450° C.,400° C., or less. In some cases, the temperature of the isothermalreactor is less than or equal to about 800° C., 750° C., 700° C., 650°C., 600° C., 550° C., 500° C., 450° C., 400° C., or less.

In some cases, the first reactor converts at least about 4%, about 5%,about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%,about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about19%, about 20%, or more of the first portion of CH₄ into C₂₊ products.In some cases, the first reactor converts between about 10% and about13% of the first portion of CH₄ into C₂₊ products. The first reactor canconvert the first portion of CH₄ into C₂₊ products with any C₂₊selectivity, including between about 55% and about 65% in someinstances.

In some cases, the first reactor has a C₂₊ yield that is at least about3%, at least about 4%, at least about 5%, at least about 6%, at leastabout 7%, at least about 8%, at least about 9%, at least about 10%, atleast about 11%, at least about 12%, at least about 13%, at least about14%, at least about 15%, or more. In some cases, the first reactor has aC₂₊ yield of between about 6% and about 9%.

In some cases, the second reactor converts at least about 15%, about16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%,about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about29%, about 30%, or more of the second portion of CH₄ into C₂₊ products.In some cases, the second reactor converts between about 20% and about22% of the second portion of CH₄ into C₂₊ products. The second reactorcan convert the second portion of CH₄ into C₂₊ products with any C₂₊selectivity, including between about 60% and about 70% in someinstances.

In some cases, the second reactor has a C₂₊ yield of at least about 8%,at least about 9%, at least about 10%, at least about 11%, at leastabout 12%, at least about 13%, at least about 14%, at least about 15%,at least about 16%, at least about 17%, at least about 18%, at leastabout 19%, at least about 20%, at least about 21%, at least about 22%,at least about 23%, or more. In some cases, the second reactor has a C₂₊yield of between about 12% and about 15%.

In some cases, a ratio of the amount of second product stream to theamount of first product stream is such that the temperature of thecombined stream is reduced below about 500° C., below about 450° C.,below about 400° C., below about 350° C., below about 300° C., or belowabout 250° C. following conversion of C₂H₆ into C₂H₄.

Systems and Methods for Heat Exchange

Several process industries, including petrochemicals and refining, makeextensive use of heat exchangers to cool and/or heat process streams(i.e., fluids) to a target temperature and/or to manage the heatgenerated and/or consumed by the process. Current heat exchangers sufferfrom many limitations, including but not limited to a change in duty andsteam production as well as a shift in exit temperature of the fluid asthe heat exchanger becomes fouled during its operation.

The present disclosure provides heat exchange devices (or apparatuses),and methods for heat exchange and systems incorporating heat exchange(e.g., for performing oxidative coupling of methane). The present heatexchangers and methods can (a) achieve high heat exchange rates until atarget temperature is reached (e.g., to quench a reaction), (b) keep theoverall duty and steam production relatively constant as the heatexchanger fouls, (c) maintain a relatively constant and high exittemperature of steam generated in cooling a process stream so as to beable to benefit from the quality of the heat (exergy) for downstreamprocesses, and (d) achieve a long service time before cleaning the heatexchanger.

Heat exchange can be performed in a variety of ways including but notlimited to counter-current flow, co-current flow and boiling, each ofwhich can have various advantages and disadvantages. FIG. 19A shows agraph of temperature versus exchanger length for counter-current flow.The process fluids may move through the heat exchanger in oppositedirections where one fluid may be heated 1900 using energy derived froma second fluid 1902. The second fluid can be cooled to a targettemperature 1904, e.g., such that a chemical reaction is quenched. Thequench rate can be proportional to the temperature difference betweenthe two fluids and is initially 1906 relatively lower forcounter-current flow compared with co-current flow and boiling, whichcan be disadvantageous when a rapid quench rate is desired. Furthermore,the exit temperature may be lower than the target temperature. Incontrast, as shown in FIG. 19B, co-current flow may have a higherinitial quench rate 1908, but a low quench rate near the exit from theexchanger 1910. Co-current exchangers can have a larger size (i.e., aremore expensive) than counter-current exchangers. Furthermore, the exittemperature may be lower than the target temperature. With reference toFIG. 19C, boiling can have a high quench rate throughout and beperformed in smaller equipment than for co-current flow. In this case,the temperature of the first fluid doesn't increase 1912 because theenergy goes to boiling the fluid. Furthermore, the exit temperature maybe lower than the target temperature.

In some cases, the apparatus and methods may use a combination ofboiling and co-current heat exchange. When the heat exchange medium iswater, the process may produce steam then super-heats the steam. Asshown in FIG. 19D, boiling 1914 and co-current heat exchange 1916 can beperformed sequentially, e.g., in two adjoining chambers of the heatexchangers described herein. This design can simultaneously achieveseveral design objectives including rapid quenching and reliably meetinga target temperature, especially as the apparatus becomes fouled overtime due to operation (e.g., deposition of material providing a heatresistance on heat exchange surfaces).

FIG. 20 is a diagram of two separate heat exchangers representing theprocess of FIG. 19D. A hot fluid, such as a process gas or processstream, may enter a first heat exchanger at an inlet 2003 and may exitthe first heat exchanger at an outlet 2005. The process gas exiting thefirst heat exchanger may subsequently enter a second heat exchanger atan inlet and exit the second heat exchanger at an outlet 2008. Heat maybe transmitted from the process gas to water contained inside a boiler,2001, to turn it into saturated steam and be conveyed to the steam drumvia riser pipes 2004. The saturated steam may exit the steam drum 2001at an outlet 2006. The saturated steam exiting the steam drum may thenenter an inlet to the second heat exchanger at an inlet. Superheatedsteam may exit the second heat exchanger at an outlet 2007. Down-comerpipe 2002 may fluidically connect the steam drum to the heat exchangerand allow saturated water that collects at the bottom of the steam drumto flow through a plurality of down-comer pipes, such as down-comer pipe2002.

FIG. 21 is a diagram of a single dual compartment heat exchanger forimplementing the process shown in FIG. 19D comprising a firstcompartment and a second compartment connected by a cross-over duct2108. A hot fluid, such as a process gas or process stream, may enterthe single heat exchanger at an inlet 2101 on a first compartment andexit the single heat exchanger at an outlet 2107 on a secondcompartment. Heat may be transmitted from the process to water containedinside a boiler to turn it into saturated steam to be conveyed to thestream drum via riser pipes. The saturated steam may exit the steam drumat an outlet 2104 on the steam drum and enter the second compartment.Superheated steam may exit the second compartment of the dual heatexchanger at an outlet 2107. A plurality of down-comer pipes, such asdown-comer pipe 2109, may fluidically connect the steam drum to the heatexchanger and allow saturated water that collects at the bottom of thesteam drum to flow through the plurality of down-comer pipes. Theapparatus can have a man-way 2103 that passes through the intermediatechannel 2102.

FIG. 22 is a diagram of an alternative to the apparatus of FIG. 20 andFIG. 21 for performing boiling followed by co-current heat exchange. Theapparatus of FIG. 22 is a dual compartment heat exchanger which that mayreduce the undesirable properties of the heat exchangers. A hot fluid,such as a process gas or process stream, may enter a single heatexchanger at an inlet 2201 on a first compartment (such as a steamgenerator) and exit the heat exchanger at an outlet 2205 on a secondcompartment (such as a super heater). Parallel or co-current flow of theprocess gas and saturated steam may occur in the second compartment ofthe heat exchanger. Heat may be transmitted from the process fluid towater contained inside a boiler to turn it into saturated steam that canbe conveyed to the steam drum via riser pipes 2206. The saturated steammay exit the steam drum 2208 at an outlet 2203 on the steam drum andenter the second compartment at an inlet. Superheated steam may exit thesecond compartment of the dual heat exchanger at an outlet 2204. Aplurality of down-comer pipes, such as down-comer pipe 2207, may connectthe steam drum to the heat exchanger and allow saturated water that maycollect at the bottom of the steam drum to flow through the down-comerpipe. A two-phase flow may enter the steam drum from the riser pipe2206.

FIG. 23 is a three panel graph plotting temperature (vertical axis withhigher temperatures at the top) of the process gas against heatexchanger length (horizontal axis with beginning of the reactor on theleft) for the combined boiling and heat exchange system shown in FIG.19D (where the two chambers are separated by a vertical line). The toppanel 2300 represents the beginning of a process run in which the systemmay be clean and have little or no fouling. In this case, (following thesolid lines) as the process gas travels along the length of the heatexchanger from an inlet to an outlet, the process gas temperature maybecome too low, such as lower than the target temperature 2302 at theoutlet of the second compartment, and there may be insufficient steamsuperheat. In some cases, more than desirable heat from the processfluid can go into boiling and less into steam super-heating. Followingthe dashed lines, the exit temperature can be corrected to match thetarget temperature by performing less boiling 2304 in the first chamber.

The middle panel 2306 represents a midpoint of a process run in whichthe system may have an intermediate amount of fouling that is the designcondition. In this case, as the process gas travels along the length ofthe heat exchanger from an inlet to an outlet, the change in process gastemperature and steam superheat temperature may be desirable. A systemwith a given amount of fouling, not heavily fouled, and not withoutfouling, may produce a desirable or optimal change in temperature acrossa length of a heat exchanger and generation of steam super-heat.

The bottom panel 2308 represents the end of a process run in which thesystem may be heavily fouled. In this case, (following the solid lines)as the process gas travels along the length of the heat exchanger froman inlet to an outlet, the process gas temperature, the tube skintemperature, and the temperature of the steam superheat may become toohigh, such as higher than the target temperature 2310 at the outlet ofthe second compartment. In some cases, less than a desirable amount ofheat from the process can go into boiling and more into steamsuper-heating. Following the dashed lines, the exit temperature can becorrected to match the target temperature by performing more boiling2312 in the heat exchanger.

FIGS. 24A-C provide examples of dual compartment heat exchangers withouta cross-over duct. These dual compartment examples combine a firstcompartment (such as a steam generator) and a second compartment (suchas a superheater with co-current flow). Positioned between the firstcompartment and the second compartment may be a thick baffle ortube-sheet 2419. This thick baffle can be different than the pluralityof baffles, such as baffle 2416, positioned within the first and secondcompartments. The plurality of baffles may be used to support the tubesor may be used as a flow guiding element, e.g., to optimize heattransmission. The thick baffle may be used to separate the boiling waterfrom the superheat steam side of the chambers and can be enhanced by aseal, by welding, by roll welding, or by explosion welding. The thickbaffle may be positioned angled (e.g., perpendicular) with respect tothe plurality of baffles within the first or second compartments. Theangle may be at least about 5°, 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70°,80° or 90°. A dual compartment heat exchanger, as shown in FIGS. 24A-C,comprising a thick baffle positioned substantially perpendicularlybetween a first and second compartments can yield changes in process gastemperature than may be suitable across a wide range of process foulingamounts. The thick baffle may be angled with respect to the first andsecond compartments. The angle may be at least about 5°, 10°, 20°, 30°,40°, 45°, 50°, 60°, 70°, 80° or 90°. For example, the systemconfiguration of FIGS. 24A-C may quench the process gas across thelength of the heat exchanger to arrive at the desired target temperatureat the outlet for a system that is clean, for a system that is heavilyfouled, and for a system that is moderately fouled.

FIG. 24A shows that a process gas may enter the dual compartment heatexchanger at an inlet 2413 on the first compartment. The process gas mayenter the heat exchanger at an initial temperature. The process gas thatenters the heat exchanger may be process gas that has recently exited anOCM unit and/or a post-bed cracking (PBC) unit. For example, the processgas that enters the heat exchange may be an OCM effluent stream. Theprocess gas may exit the dual compartment heat exchanger at an outlet2414 on the second compartment. The process gas may exit the heatexchanger at an exit temperature (e.g., of about 500° C. for OCM). Theprocess gas that exits the heat exchanger may be directed to a heater,such as a natural gas heater. The first and second compartments of theheat exchanger may comprise a plurality of baffles, such as baffle 2416.The first and/or second compartment may be over-sized to allowflexibility in operation. The first compartment of the heat exchangermay be connected to a steam drum by a plurality of down-comer pipes,such as down-comer pipe 2415 in which condensed water 2417 may enter thebottom of the boiler. Boiler feed water may enter the steam drum at aninlet 2401. A level sensor 2402 may measure the level of fluid in thesteam drum and adjust the valve at inlet 2401 to prevent the steam drumfrom overfilling or becoming empty of fluid. Saturated steam may exitthe steam drum at an outlet 2403. The saturated steam exiting the steamdrum may be split into a first and second line. The first line maydirect the saturated steam through a blast or shear atomizer 2408 andsubsequently onto to the second compartment of the heat exchanger. Thesecond line may pass the saturated steam through a valve 2404 and exitthe system at outlet 2405. Superheated steam may exit the system at anoutlet 2409 on the second compartment of the heat exchanger. Atemperature sensor 2410 may be positioned adjacent to the outlet 2409.The temperature sensor 2410 may measure the temperature of thesuperheated steam at outlet 2409 in comparison to a set temperature. Anadditional inlet flow line of boiler feed water 2406 may be added to thesystem via a valve 2407 directing the boiler feed water into the blastor shear atomizer 2408. A temperature sensor 2412 may be positionedadjacent the outlet 2414 of the second compartment. The temperaturesensor 2412 may measure the temperature of the process gas at inlet 2413in comparison to a set temperature. At high fouling rates, if theprocess gas exiting the second compartment of the heat exchanger isabove the set temperature, then more cooling duty is required viaadditional boiling. Valve 2407 may be adjusted to permit additionalboiler feed water to enter the system at inlet 2406.

At high fouling rates, the superheated steam exiting the second chambercan be above the target temperature, then the valve 2407 may be adjustedto permit additional boiler feed water to enter the system at the inlet2406. The selector 2411 can prioritize the action from the signalsprovided by the temperature sensor for the process gas 2412 and by thetemperature sensor for the superheated steam 2410.

If the process gas exiting the second compartment of the heat exchangeis below the set temperature, then less cooling duty is required. Thiscan be achieved by (a) reducing the cooling duty in the secondcompartment by arranging for a smaller steam flow to be superheated,e.g., bypassing via 2405 or (b) reducing the cooling duty in the firstchamber.

FIG. 24B shows an alternative to FIG. 24A with a dual compartment heatexchanger. FIG. 24B shows a dual compartment heat exchanger with adouble flange and gasket 2420 positioned between the first and secondcompartments.

FIG. 24C shows an alternative to FIG. 24A and FIG. 24B. Similar to FIG.24B, FIG. 24C also includes the double flange and gasket 2420 positionedbetween the first and second compartment. In addition, the system shownin FIG. 24C also splits the line of saturated steam entering the secondcompartment into a first and second line. The first line of saturatedsteam may enter the second compartment directly. The second line maypass through a restriction orifice 2421 and then into the blast or shearatomizer 2408 before entering the second compartment at inlet 2422 to bedesuperheated to some extent, with the main steam flow to besuperheated.

FIG. 25 shows the effect of fouling on the temperature of a process gasexiting a dual compartment heat exchanger with steam generation. FIG. 25plots the amount of process fouling, measured as process foulingresistance (meters squared Kelvins per Watts or m2·K/W), againsttemperature of the process gas exiting the heat recovery steam generator(HRSG). A target temperature of the process gas exiting the heatexchanger may be lower than the temperature of the process gas at theinlet to the heat exchanger. The temperature of the process gas exitingthe heat exchanger may vary with a diameter of a tube sheet, such as anouter diameter. For example, the temperature of the process gas may vary+/−50° C. over a diameter range of about 1.0 meters to about 1.5 meters.When there is no process fouling or the system is clean or the system isat a beginning of a run, the exit temperature of the process gas may bebelow a target temperature. When there is fouling present in a system,such as in the middle of a run, or the amount of process fouling isbetween about 0.005 and 0.001 m2·K/W fouling resistance, the exittemperature of the process gas may be near the design case. When thereis heavy fouling in a system, such as at the end of a run, or the amountof process fouling is between about 0.002 and 0.003 m2·K/W foulingresistance, the exit temperature of the process gas may be too high.Temperature of the process gas exiting the heat exchanger may increasewith increased process fouling.

FIG. 26 shows an example of how to operate a heat exchanger of thepresent disclosure as the heat exchanger becomes fouled. FIG. 26designates numeric indicators for differing amounts of process fouling.In this case, “level 1” indicates little or no fouling “level 4”indicates heavy fouling, and “level 2” and “level 3” are intermediatevalues. For example “level 1” can be a process fouling resistance frombetween about 0.0000 and about 0.00025 meters squared Kelvin per Watts(m2·K/W); “level 2” can be a process fouling resistance from betweenabout 0.000025 to about 0.0006 m2·K/W; “level 3” can be a processfouling resistance from between about 0.0006 to about 0.0018 m2·K/W; and“level 4” can be a process fouling resistance from between about 0.0018to about 0.003 m2·K/W.

FIG. 26 shows a table of control functions, such as valves andcontrollers that are also shown in the process diagrams of FIG. 24A-C.For example, control function <1>, as shown in the table of FIG. 26 andalso in FIG. 24A-C, may be a valve positioned between the firstcompartment and the steam drum at a middle section along the length ofthe first compartment. Control function <2>, as shown in the table ofFIG. 26 and also in FIG. 24A-C, may be a valve positioned between thefirst compartment and the steam drum at a distal end of the firstcompartment. Control functions <3a>, and <3b> may be temperaturecontrollers that act on a steam bypass valve <3>. Control function <4>may be a temperature controller that acts on boiler feed water (BFW)injection. As shown in FIG. 26, at low fouling resistance of “level 1”,valves <1> and <2> can be left in the closed position, temperaturecontrollers <3a> and <3b> can be active, and temperature controller <4>can be off. At an intermediate fouling resistance of “level 2”, valve<1> can be in the open position, valve <2> can be in the closedposition, temperature controllers <3a> and <3b> can be active, andtemperature controller <4> can be off. At an intermediate foulingresistance of “level 3”, valves <1> and <2> can be in the open position,temperature controllers <3a> and <3b> can be active, and temperaturecontroller <4> can be active. At an high fouling resistance of “level4”, valves <1> and <2> can be in the open position, temperaturecontrollers <3a> and <3b> can be off, and temperature controller <4> canbe active.

FIG. 27 shows an example of a tick baffle or tube sheet. The tube sheetmay have a labyrinth seal. The tube sheet may have a plurality ofcavities. The tube sheet may have two cavities. The tube sheet may havethree cavities. The tube sheet may have four cavities. The tube sheetmay have five or more cavities. The tube sheet may comprise a singlering per cavity. The tube sheet may comprise a plurality of rings percavity, such as two rings, three rings, four rings, or more.

System components, such as heat exchangers may be subject to foulingduring the course of a system run. The amount of fouling may change theamount of steam production. The amount of fouling may shift an exittemperature of one or both of the heat exchanging fluids, such as theprocess gas and saturated steam. Several advantages of the presentinvention may include a) achieving high quench rates of the process gasuntil reactions are frozen; b) maintaining the overall duty or steamproduction at a constant value; c) maintaining a high exit temperatureof the heat exchanging media to benefit from the quality of the heat fordownstream processes; and d) achieving a long service time betweencleaning cycles; and any combination thereof.

The dual compartment heat exchanger may be a fire-tube heat exchanger.The dual compartment heat exchanger may comprise a first compartmentcomprising a fixed boiler and a second compartment comprising a fixedsuper-heater. The fixed super-heater may comprise co-current flow of theprocess gas and saturated steam. The fixed super-heater may comprisecounter-current flow of the process gas and saturated steam.

In some cases, when the surfaces of the first compartment are clean ornon-fouled, then the steam production may be higher than a desiredamount, the process gas outlet temperature may be lower than a desiredtemperature, or a combination thereof. To reduce the amount of steamproduction, the waterside heat transfer may be reduced viasteam-pocketing one or more sections in the fixed boiler compartmentcomprising a plurality of baffles. Closing one or more valves in one ormore risers to a steam drum may prevent steam-water buoyancy to thesteam drum.

Heat exchange may be matched for all fouling conditions (clean, slightlyfouled, moderately fouled, heavily fouled), by using a co-current or aparallel heat exchanger that has a larger surface area (i.e.,overdesigned). Exit temperature of the process gas exiting the secondcompartment may be tuned by a variety of ways. For example, if thetemperature of the process gas is too high at the outlet to the secondcompartment (such as, e.g., higher than the target temperature specifiedat the outlet to the second compartment), then water may be injectedwith the feed of saturated steam at the inlet of the second compartment.The mass of injected water may be subject to boiling and superheat atthe expense of the process gas outlet temperature. If the temperature ofthe process gas at the outlet to the second compartment is low (such aslower than the target temperature specified at the outlet to the secondcompartment), then the feed of saturated steam can be reduced. With lessfeed of steam, the balance of heat exchange may shift to increase theprocess gas temperature at the outlet of the second compartment.Alternatively, if the temperature is superheated steam at the outlet istoo low (such as lower than the target temperature specified at theoutlet to the second compartment), then the feed of saturated steam maybe reduced. Reducing the feed of steam, the balance of heat exchange mayshift to increase the temperature of the superheated steam at theoutlet.

Employing systems as disclosed herein, saturated steam may besuperheated to a desired temperature, for example, at about 500° C. Thequantity and temperature of the produced superheated steam may be fairlyindifferent to the state of fouling. The process gas at the outlet mayhave a target temperature, for example, at about 500° C. for furtherprocess integration. The temperature of the process gas at the outletmay be fairly indifferent to the state of fouling.

The length of a first compartment and a second compartment of a dualcompartment heat exchanger may be same or different. The length of afirst compartment, a second compartment, or a combination thereof may beconfigured to influence a pressure drop across a dual compartment heatexchanger. The length of a first compartment, a second compartment, or acombination thereof may be configured to accommodate a wide variety ofprocess fouling and still reduce a process gas to a target temperatureat the outlet to the second compartment. The first compartment lengthmay be shorter than the second compartment length. The first compartmentlength may be about 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or less shorterin length compared to the second compartment. The first compartment maybe greater than or equal to about 2 meters (m), 3 m, 4 m, 5 m, 6 m, 7 m,8 m, 9 m, 10 m, 11 m, 12 m, 13 m, 14 m, 15 m or more in length. Thesecond compartment may be greater than or equal to about 3 meters (m), 4m, 5 m, 6 m, 7 m, 8 m, 9 m, 10 m, 11 m, 12 m, 13 m, 14 m, 15 m, 16 m, 17m, 18 m, 19 m, 20 m or more in length. In some examples, the firstcompartment may be about 4 meters in length and the second compartmentmay be about 6 meters in length.

The temperature of the process gas entering the dual compartment heatexchanger may change along the length of the exchanger. The temperatureof the process gas entering the dual compartment heat exchanger may bedifferent than the exit temperature. The temperature of the fluidentering the heat exchanger may be higher than the temperature of thefluid exiting the heat exchanger. The temperature of the fluid exitingthe heat exchanger may be about 250° C. lower than the temperature ofthe fluid entering the heat exchanger. The temperature of the fluidexiting the heat exchanger may be about 275° C. lower than thetemperature of the fluid entering the heat exchanger. The temperature ofthe fluid exiting the heat exchanger may be about 300° C. lower than thetemperature of the fluid entering the heat exchanger. The temperature ofthe fluid exiting the heat exchanger may be about 325° C. lower than thetemperature of the fluid entering the heat exchanger. The temperature ofthe fluid exiting the heat exchanger may be about 350° C. lower than thetemperature of the fluid entering the heat exchanger. The temperature ofthe fluid exiting the heat exchanger may be about 375° C. lower than thetemperature of the fluid entering the heat exchanger. The temperature ofthe fluid exiting the heat exchanger may be at least about 100° C., 125°C., 150° C., 175° C., 200° C., 205° C., 210° C., 215° C., 220° C., 225°C., 230° C., 235° C., 240° C., 245° C., 250° C., 255° C., 260° C., 265°C., 270° C., 275° C., 280° C., 285° C., 290° C., 295° C., 300° C., 305°C., 310° C., 315° C., 320° C., 325° C., 330° C., 335° C., 340° C., 345°C., 350° C., 355° C., 360° C., 365° C., 370° C., 375° C., 380° C., 385°C., 390° C., 395° C., 400° C., 425° C., 450° C., 475° C., 500° C. lowerthan the temperature of the fluid entering the heat exchanger.

The temperature of the fluid exiting the heat exchanger may be about 1%less than the temperature of the fluid entering the heat exchanger. Thetemperature of the fluid exiting the heat exchanger may be about 1.25%less than the temperature of the fluid entering the heat exchanger. Thetemperature of the fluid exiting the heat exchanger may be about 1.5%less than the temperature of the fluid entering the heat exchanger. Thetemperature of the fluid exiting the heat exchanger may be about 1.75%less than the temperature of the fluid entering the heat exchanger. Thetemperature of the fluid exiting the heat exchanger may be about 2% lessthan the temperature of the fluid entering the heat exchanger. Thetemperature of the fluid exiting the heat exchanger may be about 2.25%less than the temperature of the fluid entering the heat exchanger. Thetemperature of the fluid exiting the heat exchanger may be at leastabout 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%,1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5% less than thetemperature of the fluid entering the heat exchanger.

Control Systems

The present disclosure provides computer control systems that can beemployed to regulate or otherwise control the heat exchanger apparatus,methods and systems provided herein. A control system of the presentdisclosure can be programmed to control process parameters to, forexample, effect a given product, such as a higher concentration ofalkenes as compared to alkanes in a product stream out of an oxidativecoupling of methane (OCM) process.

FIG. 28 shows a computer system 2801 that is programmed or otherwiseconfigured to regulate heat exchange (e.g., for OCM reactions). Thecomputer system 2801 can regulate, for example, fluid stream (“stream”)flow rates, stream temperatures, stream pressures, and valve positions.

The computer system 2801 includes a central processing unit (CPU, also“processor” and “computer processor” herein) 2805, which can be a singlecore or multi core processor, or a plurality of processors for parallelprocessing. The computer system 2801 also includes memory or memorylocation 2810 (e.g., random-access memory, read-only memory, flashmemory), electronic storage unit 2815 (e.g., hard disk), communicationinterface 2820 (e.g., network adapter) for communicating with one ormore other systems, and peripheral devices 2825, such as cache, othermemory, data storage and/or electronic display adapters. The memory2810, storage unit 2815, interface 2820 and peripheral devices 2825 arein communication with the CPU 2805 through a communication bus (solidlines), such as a motherboard. The storage unit 2815 can be a datastorage unit (or data repository) for storing data.

The CPU 2805 can execute a sequence of machine-readable instructions,which can be embodied in a program or software. The instructions may bestored in a memory location, such as the memory 2810. Examples ofoperations performed by the CPU 2805 can include fetch, decode, execute,and writeback.

The storage unit 2815 can store files, such as drivers, libraries andsaved programs. The storage unit 2815 can store programs generated byusers and recorded sessions, as well as output(s) associated with theprograms. The storage unit 2815 can store user data, e.g., userpreferences and user programs. The computer system 2801 in some casescan include one or more additional data storage units that are externalto the computer system 2801, such as located on a remote server that isin communication with the computer system 2801 through an intranet orthe Internet.

The computer system 2801 can be in communication with an OCM system2830, including an OCM reactor and various process elements. Suchprocess elements can include sensors, flow regulators (e.g., valves),and pumping systems that are configured to direct a fluid.

Methods as described herein can be implemented by way of machine (e.g.,computer processor) executable code stored on an electronic storagelocation of the computer system 2801, such as, for example, on thememory 2810 or electronic storage unit 2815. The machine executable ormachine readable code can be provided in the form of software. Duringuse, the code can be executed by the processor 2805. In some cases, thecode can be retrieved from the storage unit 2815 and stored on thememory 2810 for ready access by the processor 2805. In some situations,the electronic storage unit 2815 can be precluded, andmachine-executable instructions are stored on memory 2810.

The code can be pre-compiled and configured for use with a machine havea processer adapted to execute the code, or can be compiled duringruntime. The code can be supplied in a programming language that can beselected to enable the code to execute in a pre-compiled or as-compiledfashion.

Aspects of the systems and methods provided herein, such as the computersystem 2801, can be embodied in programming. Various aspects of thetechnology may be thought of as “products” or “articles of manufacture”typically in the form of machine (or processor) executable code and/orassociated data that is carried on or embodied in a type of machinereadable medium. Machine-executable code can be stored on an electronicstorage unit, such memory (e.g., read-only memory, random-access memory,flash memory) or a hard disk. “Storage” type media can include any orall of the tangible memory of the computers, processors or the like, orassociated modules thereof, such as various semiconductor memories, tapedrives, disk drives and the like, which may provide non-transitorystorage at any time for the software programming. All or portions of thesoftware may at times be communicated through the Internet or variousother telecommunication networks. Such communications, for example, mayenable loading of the software from one computer or processor intoanother, for example, from a management server or host computer into thecomputer platform of an application server. Thus, another type of mediathat may bear the software elements includes optical, electrical andelectromagnetic waves, such as used across physical interfaces betweenlocal devices, through wired and optical landline networks and overvarious air-links. The physical elements that carry such waves, such aswired or wireless links, optical links or the like, also may beconsidered as media bearing the software. As used herein, unlessrestricted to non-transitory, tangible “storage” media, terms such ascomputer or machine “readable medium” refer to any medium thatparticipates in providing instructions to a processor for execution.

Hence, a machine readable medium, such as computer-executable code, maytake many forms, including but not limited to, a tangible storagemedium, a carrier wave medium or physical transmission medium.Non-volatile storage media include, for example, optical or magneticdisks, such as any of the storage devices in any computer(s) or thelike, such as may be used to implement the databases, etc. shown in thedrawings. Volatile storage media include dynamic memory, such as mainmemory of such a computer platform. Tangible transmission media includecoaxial cables; copper wire and fiber optics, including the wires thatcomprise a bus within a computer system. Carrier-wave transmission mediamay take the form of electric or electromagnetic signals, or acoustic orlight waves such as those generated during radio frequency (RF) andinfrared (IR) data communications. Common forms of computer-readablemedia therefore include for example: a floppy disk, a flexible disk,hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD orDVD-ROM, any other optical medium, punch cards paper tape, any otherphysical storage medium with patterns of holes, a RAM, a ROM, a PROM andEPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wavetransporting data or instructions, cables or links transporting such acarrier wave, or any other medium from which a computer may readprogramming code and/or data. Many of these forms of computer readablemedia may be involved in carrying one or more sequences of one or moreinstructions to a processor for execution.

Although systems and methods of the present disclosure have beendescribed in the context of methane and air (or oxygen), such systemsand methods may be employed for use with other hydrocarbons andoxidizing agents (e.g., NO₃, NO₂, or O₃). Non-limiting examples ofhydrocarbons include alkanes, alkenes, alkynes, aldehydes, ketones, andcombinations thereof. For instance, mixers and integrated heat exchangesof the disclosure may be employed for use with ethane, propane, pentane,or hexane. Non-limiting examples of oxidizing agents include O₂, H₂O₂,NO₃, NO₂, O₃, and combinations thereof. Moreover, although certainexamples of the present disclosure have made reference to air, otherfluids containing oxygen or an oxidizing agent (e.g., NO₂) may be used.

EXAMPLES

Below are various non-limiting examples of uses and implementations ofOCM catalysts and systems of the present disclosure.

Example 1: OCM System

FIG. 29 is a block flow diagram of a system 2900 that is configured togenerate olefins, such as ethylene. The system 2900 can be a small scaleor world scale system. The system 2900 comprises an OCM sub-system 2901that can include one or more OCM units in series and/or parallel. TheOCM sub-system 2901 can include one or more post-bed cracking (PBC)units for generating olefins (e.g., ethylene) from alkanes (e.g., ethaneand/or propane). A PBC unit can be disposed downstream of an OCM unit.The OCM unit and PBC unit can be situated in separate reactor, orincluded in the same reactor (e.g., a packed bed for OCM disposedupstream of a PBC unit in the same reactor). In some cases, anintegrated OCM unit and PBC unit may be collectively referred to as anOCM reactor.

The OCM sub-system 2901 can accept ethane and an oxidizing agent (e.g.,O₂). In the illustrated example, the OCM sub-system 2901 accepts ethanefrom ethane stream 2902 and oxygen (O₂) from oxygen stream 2903. Ethanecan be injected into the OCM sub-system 2901 at a PBC unit of the OCMsub-system 2901. Oxygen can be provided by way of air or provided froman oxygen generation unit, such as a cryogenic unit that accepts air andgenerates individual O₂ and N₂ streams, or by O₂ pipeline. The OCMsub-system 2901 also accepts methane from C₁ recycle stream 2904 andethane from C₂ recycle stream 2905.

In an OCM unit of the OCM sub-system 2901, methane can be catalyticallyreacted with oxygen in an OCM process to generate an OCM effluent stream2906 comprising C₂₊ compounds and non-C₂₊ impurities. The OCM effluentstream 2906 can be directed to a PBC unit of the OCM sub-system 2901 toconvert one or more alkanes in the OCM effluent stream 2906 to alkenes.Next, the OCM effluent stream 2906 can be directed to a process gascompressor (PGC) unit 2907. Natural gas (NG) is directed along an NGfeed 2908 to a sulfur removal unit 2909, which can removesulfur-containing chemicals from the NG feed 2908 to yield a sulfur-freemethane feed 2924 to the PGC unit 2907. As an alternative, the sulfurremoval unit 2909 can be excluded if the concentration of Sulfur in theincoming natural gas feed stream is very low and acceptable for the OCMprocess. As another alternative, the methane feed 2924 can be providedfrom other sources that may not be natural gas. In some cases, forexample if the natural gas feed has a considerable quantity of hydrogen,it can be routed to the methanation unit. From the PGC unit 2907, theOCM effluent can be directed to CO₂ removal unit 2910, which can removeCO₂ from the OCM effluent. At least a portion of the removed CO₂ can bedirected to a methanation unit 2911 along a CO₂ stream 2912. At least aportion of the removed CO₂ can be directed along CO₂ stream 2913 forother users, such as, for example, storage or purged from the CO₂removal unit 2910. In some cases, the CO₂ removal system can comprise apressure swing adsorption (PSA) unit; in other cases, the CO₂ removalsystem can be based on any other membrane separation process. Theeffluent from the CO₂ removal unit can be treated to remove water. Thewater removal system can be a molecular sieve dryer, or a series ofdryers (not shown in the figure).

Next, the OCM effluent can be directed from the CO₂ removal unit 2910 toa demethanizer (also “de-methanizer” herein) unit 2914, which canseparate methane from higher molecular weight hydrocarbons (e.g.,acetylene, ethane and ethylene). The separated (or recovered) methanecan be directed to the methanation unit 2911 along a C₁ recycle stream2915. Alternatively, or in addition to, the separated methane can bedirected to the OCM sub-system 2901. A purge stream 2923 can be directedout of the demethanizer unit 2914, which is a portion of stream 2915.The purge stream can contain methane and inert gas, such as, e.g., N₂,He or Ar. The purge flow rate may be sufficient such that the inert gaswill not accumulate in the system. The purge stream may be required toremove inert gas(es) that are built-up in the recycle loop.

The methanation unit 2911 can generate methane from CO, CO₂ and H₂.Methane generated in the methanation unit 2911 can be directed to theOCM sub-system 2901 along C₁ recycle stream 104. The methanation unit2911 can be as described elsewhere herein.

In some examples, the demethanizer unit 2914 includes one or moredistillations columns in series and/or parallel. A serial configurationcan enable the separation of different components. A parallelconfiguration can enable separation of a fluid stream of greatervolumetric flow rate. In an example, the demethanizer unit 2914comprises a distillation column and is configured to separate methanefrom C₂₊ compounds in the OCM effluent stream. The demethanizer unit2914 can be as described elsewhere herein.

Higher molecular weight hydrocarbons separated from methane in thedemethanizer unit 2914 can be directed to an acetylene conversion unit2916 along stream 2917. The acetylene conversion unit 2916 can reactacetylene (C₂H₂) in the OCM effluent with H₂ to generate ethylene. Theacetylene conversion unit 2916 in some cases can react other alkeneswith H₂ to generate alkanes, such as ethane. The acetylene conversionunit 2916 can be a hydrogenation reactor. The OCM effluent stream canthen be directed from the acetylene conversion unit 2916 to adeethanizer (also “de-ethanizer” herein) unit 2918 along stream 2919.The deethanizer unit 2918 can separate C₂ compounds (e.g., ethane andethylene) from C₃₊ compounds (e.g., propane and propylene). SeparatedC₃₊ compounds can leave the deethanizer unit 2918 along stream 2920. C₂compounds from the deethanizer unit 2918 can be directed to a C₂splitter 2921, which can separate ethane from ethylene. The C₂ splitter2921 can be a distillation column. Recovered ethylene can be directedalong stream 2922 and employed for downstream use.

OCM effluent can be characterized by a particular ethane-to-ethyleneratio or range of ratios. For example, OCM effluent can have anethane-to-ethylene ratio from about 3:1 to about 1:20. OCM effluent canhave an ethane-to-ethylene ratio of at most about 3:1, 2:1, 1:1, 1:2,1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15,1:16, 1:17, 1:18, 1:19, or 1:20.

OCM effluent can be characterized by a particular ratio or range ofratios of hydrocarbon compounds with three or more carbon atoms (“C₃₊compounds”) to C₂ compounds. For example, OCM effluent can have a C₃₊compounds-to-C₂ compounds ratio from about 0 to about 1:3. OCM effluentcan have a C₃₊ compounds-to-C₂ compounds ratio (e.g., a molar ratio) ofat least about 0, 1:1000, 1:100, 1:90, 1:80, 1:70, 1:60, 1:50, 1:40,1:30, 1:20, 1:19, 1:18, 1:17, 1:16, 1:15, 1:14, 1:13, 1:12, 1:11, 1:10,1:9, 1:8, 1:7, 1:6, 1:5, 1:4, or 1:3.

OCM effluent can be characterized by a particular acetylene-to-ethyleneratio or range of ratios. For example, OCM effluent can have anacetylene-to-ethylene ratio from about 0 to about 1:1. OCM effluent canhave an acetylene-to-ethylene ratio (e.g., a molar ratio) of at leastabout 0, 1:1000, 1:100, 1:90, 1:80, 1:70, 1:60, 1:50, 1:40, 1:30, 1:20,1:19, 1:18, 1:17, 1:16, 1:15, 1:14, 1:13, 1:12, 1:11, 1:10, 1:9, 1:8,1:7, 1:6, 1:5, 1:4, 1:3, 1:2, or 1:1.

OCM effluent can be characterized by a particular CO-to-CO₂ ratio orrange of ratios. For example, OCM effluent can have a CO-to-CO₂ ratiofrom about 0 to about 2:1. OCM effluent can have a CO-to CO₂ ratio(e.g., a molar ratio) of at least about 0, 1:1000, 1:100, 1:90, 1:80,1:70, 1:60, 1:50, 1:40, 1:30, 1:20, 1:19, 1:18, 1:17, 1:16, 1:15, 1:14,1:13, 1:12, 1:11, 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, or2:1.

Systems, methods, and processes of the present disclosure, such as thosefor OCM-ETL, operate on feedstocks with particular ethane-to-methaneratios. For example, a system feedstock can have an ethane-to-methaneratio from about 0 to about 1:3. A system feedstock can have anethane-to-methane ratio (e.g., a molar ratio) of at least about 0,1:1000, 1:100, 1:90, 1:80, 1:70, 1:60, 1:50, 1:40, 1:30, 1:20, 1:19,1:18, 1:17, 1:16, 1:15, 1:14, 1:13, 1:12, 1:11, 1:10, 1:9, 1:8, 1:7,1:6, 1:5, 1:4, or 1:3.

The systems of the present disclosure, such as the system of FIG. 29,can be suited for the production of any olefin, such as, for example,ethylene. Thus, the systems above and elsewhere herein are not limitedto ethylene but may be configured to generate other olefins, such aspropylene, butenes, pentene, or other alkenes.

Post-bed cracking (PBC) units that may be suitable for use with systemsof the present disclosure, such as the system of FIG. 29, are describedin, for example, U.S. Patent Publication No. 2015/0152025, which isentirely incorporated herein by reference.

The system of FIG. 29 may employ different unit operations for smallscale and world scale olefin production (e.g., ethylene production). Thepresent disclosure provides non-limiting example unit operations andprocess flows for various units that may be employed for use with thesystem of FIG. 29.

Example 2: Implementation of OCM

About 1,000,000 metric tons/year of polymer grade ethylene is producedvia the oxidative coupling of methane (OCM). The OCM reactor comprises a2-stage adiabatic axial fixed bed that utilizes an OCM catalyst (e.g.,nanowire catalyst) to convert methane and high purity oxygen toethylene. The methane feed to the OCM reactor is the recycle stream froma downstream demethanizer over-head supplemented by CO and CO₂conversion to methane in a two-stage methanation reactor. The hot OCMeffluent from a second stage of the reactor effluent is mixed withheated recycle ethane from a downstream C₂ splitter and cracked toconvert ethane primarily into ethylene. Hot reactor effluent is used toheat OCM reactor feed, generate high-pressure steam and heat processcondensate. Cold reactor effluent is compressed and mixed withsulfur-free pipeline natural gas and treated to remove CO₂ and H₂O priorto cryogenic separations. The treated process gas is fed to ademethanizer column to recover about 99% of ethylene as column bottomsstream. Demethanizer bottoms steam is separated in deethanizer column toseparate C₂'s from C₃₊ components. Deethanizer column overhead is firsttreated in selective hydrogenation unit to convert acetylene intoethylene and ethane using H₂ from a Pressure Swing Adsorption (PSA)Unit. The resulting stream is separated in a C₂ splitter unit toseparate ethylene from ethane. Deethanizer bottoms stream is sent to aDe-propanizer to obtain Refinery Grade Propylene (RGP) and mixed C₄₊stream, both which can be sold for credit. Ethane product stream from C₂splitter bottoms is recycled to second stage of the OCM reactor tocomplete extinction. Polymer grade ethylene product (99.96 wt %ethylene) obtained from the C₂ splitter overhead is compressed to 1,000psig and exported as vapor product. A stream factor of 0.95 is used(equal to an installed capacity of 1,059,000 metric tons/yr).

The OCM process generates superheated high pressure (1500 psia) steamthat is used to run process gas compressors, refrigeration compressors,ethylene heat pump/product compressors, and major pumps. The remainderof the steam and small portion of recycle methane (purge gas) can beexported to combined cycle/gas turbine system to generate power. The OCMprocess has an energy intensity of about −0.89 MMBTU/MT ethylene, whilethe energy intensity of a comparably sized steam cracking of ethaneprocess is about 31.89 MMBTU/MT.

The reactor consists of a 2-stage adiabatic axial fixed bed withintermediate heat recovery via high-pressure steam generation. Themethane stream recycled from the demethanizer overhead becomes the mainOCM reactor feed. In both stages high purity oxygen is mixed with thehydrocarbon stream in a proportion of approximately 1:10 on a molarbasis to achieve the optimal O₂-limited composition for the OCMreaction.

In the OCM reactor, the catalyst enables the partial and highlyselective conversion of methane to, primarily, ethylene and ethane, withminor amounts of propylene and propane. Non-selective pathways includehigh temperature hydrocarbon reactions, such as combustion, reformingand shift. The second stage of the reactor may be configured toaccommodate an ethane conversion zone immediately downstream of thecatalytic bed. Ethane recycled from the deethanizer and, optionally,additional fresh ethane feed are injected into this reactor sectionwhere ethane undergoes highly selective adiabatic thermalde-hydrogenation to ethylene.

The OCM reactor effluent flows through a series of heat exchangers toachieve optimal heat recovery and final condensation at ambienttemperature, prior to being sent to the Process Gas Compressor (PGC).The natural gas feed stream is mixed with the OCM reactor effluent atthe PGC delivery. Gas treating, including CO₂ removal and drying,follows the compression step. The product recovery train consists of ademethanizer, deethanizer, acetylene converter and C₂ splitterconfiguration where the refrigeration and heat integration scheme may beconfigured to optimize heat recovery and minimize power consumption. Theproduct streams comprise of polymer grade ethylene and a C₃₊ mixedstream, similar in composition to Refinery Grade Propylene (RGP), whichcan be optionally further separated and purified. The C₁ recycle streamleaving the demethanizer head is sent to a conventional methanation unitwhere all CO and a portion of the CO₂ product react with hydrogen toform methane. The integration of the methanation unit into the overallprocess may be instrumental to maximizing the carbon efficiency of theOCM technology.

The OCM process may be energy neutral. The OCM reaction heat is utilizedto provide mechanical power to the rotating units required forcompression and pumping. The OCM process gets pure oxygen from anadjacent Air Separation Unit (ASU) which also houses a Gas TurbineCombined Cycle (GTCC). The GTCC unit is fed with the purge gas extractedfrom the demethanizer overhead and provides all the mechanical power andsteam required by the ASU.

The final products are 1,000,000 metric tons per annum of polymer gradeethylene and 88,530 metric tons per annum of C₃₊ hydrocarbons. The C₃₊hydrocarbons are sent to a depropanizer to obtain refinery gradepropylene (65% propylene) as distillate.

Example 3: Dual Compartment Heat Exchanger

A dual compartment heat exchanger reduces a process gas temperature from830° C. to 500° C. Specifically, a process gas exiting a post-bedcracking unit enters a first compartment of a dual compartment heatexchanger. The process gas may travel along the length of the firstcompartment, across a tube-sheet positioned substantiallyperpendicularly between the first and second compartments, into thesecond compartment, and exits the second compartment at an outlet. Thetube sheet has a thickness of 50 millimeters. The process gas thatenters the first compartment has a temperature of 830° C. The processgas that exits the second compartment has a temperature equal to atarget temperature of 500° C. A steam drum is positioned adjacent to thefirst compartment for generating saturated steam. The saturated steamgenerated by the steam drum enters the second compartment and travels inco-current flow to the process gas and facilitates further cooling ofthe process gas. The first compartment is 4 meters in length. The secondcompartment is 6 meters in length. At the beginning of the run, theprocess fouling resistance is 0 meters squared Kelvin/Watts (m2·K/W). Atthe end of the process run, the process fouling resistance is 0.003m2·K/W. The thermal conductivity of the tube sheet is 0.5 Watts permeter Kelvin (W/mK).

It should be understood from the foregoing that, while particularimplementations have been illustrated and described, variousmodifications can be made thereto and are contemplated herein. It isalso not intended that the invention be limited by the specific examplesprovided within the specification. While the invention has beendescribed with reference to the aforementioned specification, thedescriptions and illustrations of the preferable embodiments herein arenot meant to be construed in a limiting sense. Furthermore, it shall beunderstood that all aspects of the invention are not limited to thespecific depictions, configurations or relative proportions set forthherein which depend upon a variety of conditions and variables. Variousmodifications in form and detail of the embodiments of the inventionwill be apparent to a person skilled in the art. It is thereforecontemplated that the invention shall also cover any such modifications,variations and equivalents. It is intended that the following claimsdefine the scope of the invention and that methods and structures withinthe scope of these claims and their equivalents be covered thereby.

What is claimed is:
 1. A method for producing butadiene, comprising: (a)directing methane (CH₄) and oxygen (O₂) into an oxidative coupling ofmethane (OCM) reactor that permits the CH₄ and the O₂ to react to yieldan OCM product stream comprising hydrogen (H₂), carbon monoxide (CO),carbon dioxide (CO₂), unreacted CH₄, and hydrocarbon compounds with twoor more carbon atoms (C₂₊ compounds), including ethylene; (b) directingat least a portion of the OCM product stream into a dimerization reactorthat permits at least a portion of the ethylene to react to produce adimerization product stream comprising butene-1; and (c) directing thedimerization product stream into a C₄ dehydrogenation reactor thatconverts the butene-1 to butadiene.
 2. The method of claim 1, furthercomprising recycling unreacted ethylene to the dimerization reactor. 3.The method of claim 1, wherein the CH₄ is provided by a streamcomprising natural gas.
 4. The method of claim 1, further comprisingdirecting a stream comprising ethane to a post-bed cracking zone of theOCM reactor.
 5. The method of claim 1, further comprising recovering alights stream comprising at least a portion of the hydrogen (H₂), carbonmonoxide (CO), carbon dioxide (CO₂), and unreacted CH₄ from the OCMproduct stream, and directing the lights stream into a methanationreactor to form a methanated stream comprising CH₄.
 6. The method ofclaim 5, further comprising directing the methanated stream into the OCMreactor.
 7. The method of claim 1, wherein the dimerization reactorcontains a catalyst comprising titanium.
 8. The method of claim 1,wherein at least a portion of the O₂ directed into the OCM reactor isprovided from an air separation unit that extracts O₂ from air.
 9. Themethod of claim 1, further comprising cooling the OCM product stream ina heat exchanger downstream of the OCM reactor.
 10. The method of claim9, wherein the heat exchanger is a heat recovery steam generator thatgenerates high pressures steam.
 11. A method for performing an oxidativecoupling of methane (OCM) reaction, comprising: (a) heating a firststream comprising oxygen (O₂) to a first temperature; (b) dividing asecond stream comprising methane (CH₄) into at least two portions andheating each of the at least two portions to a different temperature;(c) directing the each of the at least two portions of the second streaminto a different area of a mixer, which mixer mixes the CH₄ with thefirst stream to generate mixtures; and (d) contacting the mixturesgenerated in (c) with an OCM catalyst bed to perform the OCM reaction.12. The method of claim 11, wherein the first stream is air.
 13. Themethod of claim 11, wherein the second stream is natural gas.
 14. Themethod of claim 11, wherein areas of the mixer into which the at leasttwo portions of the second stream are directed in (c) are selected toreduce a maximum temperature of the OCM catalyst bed during the reactionin (d).
 15. The method of claim 11, wherein areas of the mixer intowhich the at least two portions of the second stream are directed in (c)are selected to bypass a portion of the O₂ further into the OCM catalystbed.
 16. A method for performing an oxidative coupling of methane (OCM)reaction, comprising: (a) heating a first stream comprising methane(CH₄) to a first temperature; (b) dividing a second stream comprisingoxygen (O₂) into at least two portions and heating each of the at leasttwo portions to a different temperature; (c) directing the each of theat least two portions of the second stream into a different area of amixer, which mixer mixes the O₂ with the first stream; and (d)contacting the mixtures produced in (c) with an OCM catalyst bed toperform the OCM reaction.
 17. The method of claim 16, wherein the firststream is natural gas.
 18. The method of claim 16, wherein the secondstream is air.
 19. The method of claim 16, wherein areas of the mixerinto which the at least two portions of the second stream are directedin (c) are selected to reduce a maximum temperature of the OCM catalystbed during the reaction in (d).
 20. The method of claim 16, whereinareas of the mixer into which the at least two portions of the secondstream are directed in (c) are selected to bypass a portion of the O₂further into the OCM catalyst bed.